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THE   RISE   AND    DEVELOPMENT 


OF 


THE    LIQUEFACTION    OF    GASES 


THE 


RISE  AND  DEVELOPMENT 


OF  THE 


LIQUEFACTION    OF    GASES 


BY 


WILLETT   L.    HARDIN,  PH.D. 

HARRISON  SENIOR   FELLOW    IN    CHEMISTRY  IN  THB 
UNIVERSITY  OF  PENNSYLVANIA 


THE    MACMILLAN    COMPANY 

LONDON  :    MACMILLAN  &  CO.,  LTD. 

!9°5 

^//  rights  reserved 


COPYRIGHT,  1899, 
BY  THE  MACMILLAN   COMPANY. 


Set  up  and  electrotyped.      Published  August,  1899.      Reprinted 
March,  1905. 


PREFACE 

RECENT  developments  in  the  liquefaction  of  air 
and  the  recent  liquefaction  of  hydrogen  have 
added  considerable  interest  to  the  whole  subject 
of  the  liquefaction  of  gases.  The  literature  on 
this  subject  is  scattered,  for  the  most  part,  in 
foreign  journals,  and  is  inaccessible  to  a  majority 
of  those  who  are  interested  in  scientific  work. 

The  object  of  this  little  volume  is  to  present 
a  complete  history  of  the  development  of  the 
methods  employed  in  the  liquefaction  of  gases. 
Sufficient  theory  has  been  given  to  enable  the 
popular  reader  to  understand  the  principles  in- 
volved. While  the  book  has  been  written  in  a 
popular-science  style,  an  effort  has  been  made  to 
make  it  of  value  to  those  who  are  especially 
interested  in  the  subject  by  giving  the  references 
to  the  original  literature. 

The  first  intention  was  to  include  a  complete 
account  of  researches  at  low  temperatures  and 
of  the  industrial  applications  of  liquefied  gases. 

V 

224539 


vi  PREFACE 

This,  however,  would  make  the  work  unduly 
large,  and  for  that  reason  these  subjects  are  con- 
sidered only  in  a  general  way. 

Full  credit  has  been  given  throughout  the  book 
to  the  various  sources  of  information.  In  conclu- 
sion I  desire  to  express  my  obligations  to  Mr. 
Louis  M.  Thorn  for  the  care  which  he  has  taken 
in  the  preparation  of  the  drawings,  and  also  to 
Professor  Edgar  F.  Smith  for  his  kindness  in 
reading  the  manuscript  and  for  many  valuable 
suggestions. 

W.  L.  HARDIN. 

APRIL,  1899. 


CONTENTS 


INTRODUCTION 


CHAPTER   I 


Introduction  of  the  term  "gas"  —  Distinction  between 
gases  and  vapors  —  Guericke's  air-pump  —  Experi- 
ments of  Boyle  and  Mariotte  on  the  compression  of 
gases  —  Influence  of  temperature  on  gaseous  volume 
—  Absolute  temperature  —  Early  experiments  on 
the  liquefaction  of  gases  —  Vaporization  of  liquids 
in  closed  tubes  by  Cagnaird  de  la  Tour  ...  5 

CHAPTER   II 

Liquefaction  of  gases  by  Faraday  —  Attempt  to  liquefy 
air  by  Perkins  —  Experiments  of  Bussy  —  Evapora- 
tion of  liquids  as  a  means  of  lowering  the  tempera- 
ture —  Heat  of  vaporization  —  Attempt  to  liquefy 
air  by  Colladon—  Liquefaction  and  solidification 
of  carbonic  acid  by  Thilorier  —  Application  of  solid 
carbonic  acid  and  ether  to  the  production  of  low 
temperatures  —  Sinking  of  gases  to  great  depths  in 
the  ocean  —  Second  series  of  experiments  by  Fara- 
day —  Experiments  of  Natterer  —  Observations  of 
Berthelot,  Drion,  and  Mendeleeff  —  Exceptions  to 
Boyle's  law  ........  22 

CHAPTER   III 

Experiments  of  Andrews  on  carbonic  acid  —  Introduc- 
tion of  critical  constants  —  Determination  of  critical 
vii 


viii  CONTENTS 


constants  —  Critical  constants  of  gaseous  mixtures 
— Continuity  of  the  gaseous  and  liquid  states  of 
matter —  Condition  of  matter  at  the  critical  point  — 
Exceptions  to  Boyle's  law  —  Kinetic  theory  of  gases 
—  Relation  between  the  gaseous  and  liquid  states 
as  expressed  by  the  equation  of  Van  der  Waals  .  70 

CHAPTER   IV 

Liquefaction  of  the  so-called  permanent  gases  by  Caille- 
tet  and  Pictet — Liquefaction  of  ozone  —  Liquefac- 
tion and  determination  of  boiling  points  and  critical 
constants  of  oxygen,  air,  nitrogen,  etc.,  by  Wroblew- 
ski,  Olszewski,  and  Dewar  —  Solidification  of  the 
so-called  permanent  gases  —  Dewar  vacuum  bulbs 

—  Researches  at  low  temperatures  —  Experiments 
of  Kamerlingh-Onnes  —  History  of  the  regenera- 
tive method  of  refrigeration  —  Application  of  this 
method  in  the  liquefaction  of  oxygen,  air,  nitrogen, 
etc.,  by  Linde,  Hampson,  Dewar,  and  Tripler  — 
Theory  of  the  regenerative  method  of  refrigeration 

—  Liquefaction    and    solidification    of    argon    by 
Olszewski  —  Attempt   to    liquefy   helium  —  Lique- 
faction of  fluorine  by  Moissan  and  Dewar  —  Lique- 
faction   of    hydrogen    and    helium    by    Dewar  — 
Experiments  on  krypton,  metargon,  and  neon  — 
The  supposed  new  gas  etherion  —  Table  of  physi- 
cal constants  .         -113 

CONCLUSION 

The  three  states  of  matter — Industrial  application  of 
liquefied  gases  —  Physiological  action  at  low  tem- 
peratures —  Properties  of  matter  at  low  temperatures  23 1 


"CONSIDER  for  a  moment  what  would  happen  to  the  dif- 
ferent substances  which  compose  the  globe,  if  its  temperature 
should  be  suddenly  changed.  Suppose,  for  instance,  that  the 
earth  .  .  .  should  be  suddenly  placed  in  a  very  cold  region, 
...  —  the  water  which  at  present  forms  our  rivers  and  seas, 
and  probably  a  majority  of  the  liquids  which  are  known, 
would  be  transformed  into  solid  mountains.  On  this  suppo- 
sition the  air,  or  at  least  a  part  of  the  aeriform  substances 
which  compose  it,  would  doubtless  cease  to  exist  in  the  state 
of  an  invisible  fluid,  for  want  of  a  sufficient  degree  of  heat ; 
it  would  return  to  the  liquid  state,  and  this  change  would 
produce  new  liquids  of  which  we  have  no  knowledge." 

LAVOISIER  (1784). 


LIQUEFACTION    OF   GASES 

INTRODUCTION 

PROBABLY  no  line  of  scientific  research  has  been 
more  productive  of  ingenious  experiments  or  more 
prolific  of  results  than  that  of  the  liquefaction  of 
gases.  To  convert  ordinary  air  into  a  liquid  or 
even  a  solid  is  to-day  a  matter  of  little  difficulty. 
So  great  an  achievement,  however,  is  not  the  work 
of  a  single  individual  or  the  product  of  a  single 
generation.  It  is  a  result  of  the  combined  efforts 
of  numerous  experimenters,  and  represents  the 
progress  of  a  century. 

The  development  of  the  methods  has  been  ac- 
companied by  many  fruitless  and  discouraging 
observations.  The  experiments  have  been  of  such 
a  nature  as  to  require  the  application  of  consider- 
able pressure.  Vessels  of  exceedingly  brittle  glass 
were  used  in  most  cases,  and  many  explosions 
resulted.  There  was  also  a  great  expense  attached 
to  experiments  of  this  nature.  Within  recent  years 
various  metals  and  alloys  have  been  substituted 
for  glass  in  the  construction  of  apparatus.  Pictet 

B  I 


OF   GASES 

Vays1  t&afc  'modern*  rhetariurgy  has  greatly  aided  in 
the  construction  of  pressure-vessels.  The  present 
high  grade  of  steel  is  almost  indispensable. 

Notwithstanding  the  fact  that  the  difficulties 
to  be  overcome  were  enormous,  and  that  the  ex- 
perimenters were  subjected  to  considerable  danger, 
the  investigations  have  been  carried  on  with 
untiring  zeal.  The  history  of  the  liquefaction  of 
gases,  like  that  of  other  lines  of  scientific  research, 
is  marked  with  periods  of  unusual  activity  and 
rapid  progress.  These  periods  of  enthusiasm  were 
sometimes  followed  by  a  few  years  of  quiet,  un- 
eventful observations.  The  announcement  of  a 
new  discovery,  however,  was  always  sufficient  to 
give  a  new  impetus  to  the  work. 

In  tracing  the  development  of  the  methods  em- 
ployed in  the  liquefaction  of  gases,  it  is  perhaps 
advisable  to  divide  the  work  into  four  periods. 
The  four  chapters  of  this  volume  correspond  to 
these  periods. 

The  first  chapter  is  concerned  with  the  early 
history  of  the  subject.  In  this  period  some  of  the 
earlier  observations  on  the  compression  of  gases, 
and  likewise  a  few  disconnected  experiments  on 
the  liquefaction  of  gases,  are  considered.  These 
investigations  are  only  of  historical  interest,  and 
hence  are  only  briefly  outlined. 

The  second  chapter  begins  with  the  work  of 


INTRODUCTION  3 

Faraday  (1823),  and  embraces  nearly  half  a  century 
of  fruitful  observations.  The  fundamental  methods 
for  obtaining  high  pressures  and  low  temperatures 
were  developed  to  a  comparatively  high  degree 
during  this  period.  Carbonic  acid,  nitrous  oxide, 
ammonia,  etc.,  were  liquefied  and  solidified  dur- 
ing this  time. 

The  third  chapter  is  devoted  to  critical  con- 
stants, and  the  continuity  of  the  gaseous  and 
liquid  states  of  matter.  The  experiments  of  An- 
drews form  the  first  and  most  important  division 
of  this  chapter.  These  observations  mark  the 
beginning  of  a  new  epoch  in  the  liquefaction  of 
gases.  A  brief  account  is  also  given  of  some 
experiments  which  have  been  made  with  a  view  of 
determining  the  condition  of  matter  at  the  critical 
point.  The  equation  of  Van  der  Waals  is  likewise 
briefly  considered. 

The  fourth  period  begins  with  the  liquefaction 
of  the  so-called  permanent  gases  by  Cailletet  and 
Pictet  (1877),  and  extends  to  the  present  time. 
During  this  period  the  apparatus  employed  in  the 
liquefaction  of  gases  has  been  perfected  to  a  very 
high  degree.  The  chapter  is  divided  into  four 
sections  as  follows  :  — 

i.  The  pioneer  experiments  of  Cailletet  and 
Pictet  on  the  liquefaction  of  the  so-called  perma- 
nent gases  (1877-1882). 


4  LIQUEFACTION   OF   GASES 

2.  The  experiments  of  Wroblewski,  Olszewski, 
and  Dewar  from   1883  to  1895.     This  work  may 
be  considered  as  supplementary  to  that  of  Caille- 
tet  and  Pictet. 

3.  Liquefaction  of  gases   by   the   regenerative 
method. 

4.  Liquefaction    of    argon,    hydrogen,    helium, 
etc.     The  section  closes  with  a  table  of  physical 
constants. 

This  chapter,  which  extends  over  a  period  of 
only  two  decades,  occupies  more  than  one  half  of 
the  present  volume. 

In  the  conclusion  the  three  states  of  matter  are 
briefly  compared,  and-  their  similarities  pointed 
out.  Reference  is  also  made  to  various  industrial 
applications  of  liquefied  gases.  Great  advance  in 
this  direction  seems  imminent  from  the  recent 
progress  in  the  liquefaction  of  gases.  A  short 
account  is  next  given  of  physiological  action,  and 
the  properties  of  matter  at  low  temperatures. 
Here  again  we  may  look  forward  to  great  achieve- 
ments. The  high  pressures  and  low  temperatures 
which  can  be  obtained  by  means  of  liquid  air,  etc., 
have  opened  up  new  fields  of  research  in  every 
branch  of  natural  and  physical  science. 


CHAPTER    I 

EARLY   HISTORY 

THE  fact  has  long  been  known  that  many  liquids 
can  be  converted  into  vapors  which  are  similar,  in 
most  respects,  to  ordinary  gases.  It  has  been 
equally  well  known  that  the  vapors  thus  produced 
can  be  condensed  to  the  original  liquids  by  lower- 
ing the  temperature.  These  phenomena  at  once 
suggest  an  intimate  relation  between  the  gaseous 
and  liquid  states  of  matter.  Some  believed  that 
the  possibility  of  condensation  applied,  not  only  to 
certain  vapors,  but  to  all  gases.  Before  the  com- 
position of  the  atmosphere  was  known,  attempts 
were  made  to  condense  it  to  a  liquid. 

Some  of  the  experiments  which  are  considered 
in  this  chapter  were  made,  not  with  a  view  of  con- 
densing the  gas,  but  for  the  purpose  of  studying 
the  influence  of  temperature  and  pressure  on  gas- 
eous volume.  The  results  in  many  cases,  however, 
have  an  important  bearing  on  the  liquefaction  of 
gases. 

Experiments  on  the  pneumatic  applications  of 
compressed  air  were  made  before  the  Christian 

5 


6  LIQUEFACTION   OF   GASES 

era.  These  observations,  and  many  other  experi- 
ments on  compressed  gases,  may  be  omitted  in  a 
work  of  this  nature. 

For  the  present  purpose  we  may  begin  with  the 
observations  of  Van  Helmont1  in  the  latter  part  of 
the  sixteenth  and  the  early  part  of  the  seventeenth 
century.  He  made  the  first  great  advance  in  the 
study  of  gases.  He  introduced  the  term  "gas," 
and  applied  it  to  bodies  which  are  similar  to  or- 
dinary air.  'It  is  evident  that  the  problem  of  con- 
densing gases  to  the  liquid  state  also  occurred  to 
him,  for  he  was  the  first  to  distinguish  between 
gases  and  vapors ;  the  latter,  he  said,  can  be  con- 
densed to  the  liquid  state,  while  the  former  cannot. 
This  distinction  remained  unquestioned  for  nearly 
two  centuries.  When  we  consider  that  experi- 
ments on  distillations  occupied  fifty  years  of  Van 
Helmont's  life,2  we  can  understand  these  state- 
ments, which,  in  reality,  are  far  in  advance  of  the 
age  in  which  he  lived. 

About  the  middle  of  the  seventeenth  century 
Guericke3  constructed  an  air-pump.  This  ap- 
paratus, in  its  simplest  form,  consisted  of  a  ver- 
tical brass  cylinder,  which  was  provided  with  a 
movable  piston.  By  means  of  this  pump,  he 

1  Kopp,  Geschichte  der  Chemie,  I,  pp.  121-122. 

2  Boerhaave,  Elements  of  Chemistry,  Eng.  ed.,  I,  p.  16. 
8  Haiiy,  Nat,  Philos.,  Eng.  ed.,  p.  220. 


EARLY    HISTORY  7 

studied  the  influence  of  pressure  on  the  volume 
of  a  given  quantity  of  air.  The  principle  of 
Guericke's  air-pump  has  been  applied  by  numer- 
ous experimenters  in  their  study  of  compressed 
gases. 

The  first  systematic  observations  on  the  influence 
of  pressure  on  the  volume  of  a  gas  are  those  of 
Boyle.  In  1662  he  announced  an  important  law, 
which  bears  his  name.  He  stated  that  the  volume 
of  a  gas  varies  inversely  as  the  pressure.  In  other 
words,  the  product  of  the  pressure  and  volume  is 
a  constant.  The  law  is  usually  expressed  by  the 
equation 

pv  =  c, 

where  c  is  a  constant.  The  same  law  was  an- 
nounced by  Mariotte  a  few  years  later.  The  con- 
ditions under  which  gases  deviate  from  this  law 
will  be  considered  in  a  subsequent  chapter. 

From  the  writings  of  Boerhaave  (1731),  it  is 
evident  that  he  had  considered  the  problem  of 
liquefying  and  of  solidifying  ordinary  air.  In  the 
English  edition  of  his  Elements  of  Chemistry,  pp. 
249,  250,  we  find  the  following  statement  :  — 

"  The  first  property,  then,  of  air  which  offers 
itself  to  our  consideration  is  its  fluidity.  This  is 
so  natural  to  it  that  I  do  not  remember  ever  to 
have  heard  of  any  experiment  by  which  air  could 
be  deprived  of  it.  It  is  evident  to  every  one's 


8  LIQUEFACTION   OF   GASES 

observation  that  even  in  the  sharpest  frost,  when 
almost  everything  is  congealed,  the  air  still  re- 
mains fluid  ;  nay,  in  an  artificial  cold,  40°  greater 
than  nature  has  ever  been  known  to  produce,  the 
air  still  retained  its  fluidity.  ...  If  you  compress 
the  air,  with  ever  so  great  weight  and  force,  into 
the  utmost  density,  it  does  not  then  become  solid 
by  concretion,  but  remains  equally  fluid  as  before. 
...  I  have  never  yet  met  with  a  single  experiment 
by  which  it  appeared  that  air  was  coagulated  into 
a  solid  mass.  I  confess  that,  one  noon  in  frosty 
weather,  when  the  air  was  very  serene,  I  observed 
some  very  small  corpuscles  floating  about  in  it.  ... 
But,  after  a  careful  observation,  I  discovered  that 
these  were  nothing  but  little  globules  of  water, 
which  were  congealed,  and  which  appeared  in  the 
form  of  a  very  subtle  hoar-frost." 

In  speaking  of  the  elasticity  of  the  air,  the  same 
writer,  pp.  263-264,  says  :  — 

"  Another  law  which  we  find  to  hold  true  is,  that 
the  elasticity  of  the  air  cannot  be  destroyed.  . 
In  whatsoever  manner  the  air  has  been  com- 
pressed by  the  utmost  power  of  weights,  it  has 
always  remained  very  fluid ;  for,  after  it  has  been 
contracted  into  the  greatest  density,  it  has  con- 
stantly restored  itself  again  into  all  its  particles, 
so  as  to  fill  up  exactly  the  former  space  ;  all  parti- 
cles retreating  with  the  same  ease  with  which  they 


EARLY   HISTORY  9 

came  together.  .  .  .  We  may  fairly  assert  that 
the  fluidity  of  the  air  in  all  the  large  compass, 
from  the  most  rarefied  to  the  most  compressed, 
remains  without  alteration ;  and  that  therefore  it  is 
neither  capable  of  being  solidified  by  the  intensest 
cold,  nor  the  greatest  degree  of  compression." 

On  page  266  of  the  same  book  we  find  that 
Boerhaave  was  familiar  with  the  fact  that  heat 
expands  the  air.  The  following  are  his  words  :  — 

"  By  the  application  of  fire  the  air  becomes  so 
rare  that  neither  the  measure  nor  limit  of  its  dila- 
tion has  yet  been  discovered.  .  .  .  Air  of  unequal 
masses,  but  of  the  same  density,  is  always  ex- 
panded in  the  same  measure  by  the  same  degree 
of  fire :  so  that  these  expansions  in  the  same 
density  of  air  are,  by  a  constant  law  of  nature, 
always  proportional  to  the  augmentations  of 
heat." 

As  early  as  1 702  Amontons l  studied  the  effect 
of  temperature  on  the  elastic  force  of  the  air.  He 
says :  "  If  equal  or  unequal  masses  of  air  are 
charged  with  equal  weights,  their  elastic  forces 
will  be  equally  increased  by  equal  degrees  of 
heat." 

In   1787  Charles2  called  attention  to  the  fact 

1  Haiiy,  Nat.  Philos.,  Eng.  ed.,  pp.  255-260. 

2  Charles  communicated  his  results  to  Gay  Lussac  and  did  not 
publish  them. 


TO  LIQUEFACTION   OF  GASES 

that  all  gases  expand  equally  with  the  same  in- 
crease in  temperature.  Dalton1  made  similar 
observations  in  1801.  He  is  also  the  author  of  the 
following  statement : 2  "  There  can  scarcely  be 
a  doubt  entertained  respecting  the  reducibility  of 
all  elastic  fluids  of  whatever  kind  into  liquids ;  and 
we  ought  not  to  despair  of  effecting  it  in  low 
temperatures,  and  by  strong  pressures  exerted 
upon  the  unmixed  gases."  Dalton,  just  as  La- 
voisier, foresaw  the  result  of  subjecting  gases  to 
intense  cold. 

The  relation  of  temperature  to  the  volume  of 
a  gas  was  more  thoroughly  investigated  by  Gay 
Lussac  in  1802.  From  his  results,  as  well  as 
from  those  of  Dalton  and  Charles,  we  find  that  an 
increase  of  i°  in  temperature3  increases  the  vol- 
ume of  a  gas  by  about  %]%  of  the  volume  at  o°, 
provided  the  pressure  remains  constant.  In  other 
words,  the  volume  v  of  a  gas  at  the  temperature  / 
is  given  by  the  equation, 


where  VQ  represents  the  volume  at  o°.     In  various 

1  Manchester  Memoirs,  V,  p.  535,  1801.  Ref.  Roscoe  and  Schor- 
lemmer,  Chemistry,  I,  p.  60,  1895. 

*  Ref.  Dewar,  Proc.  Roy.  /;«/.,  8,  p.  657,  1878. 

8  All  temperatures  will  be  given  in  Centigrade  degrees  unless 
otherwise  expressed. 


EARLY    HISTORY  11 

text-books,  this  law  is  referred  to  as  the  law  of 
Charles,  the  law  of  Dalton,  or  the  law  of  Gay 
Lussac,  depending  upon  the  author  of  the  book. 
According  to  this  law  all  gases  have  the  same 
coefficient  of  expansion  with  regard  to  tempera- 
ture. In  this  respect  the  gaseous  state  of  matter 
stands  alone ;  the  coefficients  of  expansion  of 
liquids  and  solids  show  considerable  variation. 

Absolute  Temperature. 

Throughout  the  discussion  of  the  experiments 
on  the  liquefaction  of  gases,  reference  will  fre- 
quently be  made  to  absolute  temperature.  The 
significance  of  this  term  may  be  best  understood 
by  considering  the  law  of  Gay  Lussac.  Suppose 
we  start  with  a  given  volume  of  gas  at  o°.  Let 
the  pressure  remain  constant.  If  the  tempera- 
ture be  increased  to  273°,  the  volume  will  be 
doubled.  If,  on  the  other  hand,  the  temperature 
be  lowered,  the  volume  will  be  decreased  by  ^3 
of  the  original  volume  for  each  degree  of  tem- 
perature change.  If  the  law  remains  valid  for 
all  temperatures,  an  important  conclusion  fol- 
lows; namely,  at  the  temperature  of  —  273°  the 
volume  of  the  gas  will  become  equal  to  zero. 
Of  course,  it  is  not  likely  that  such  a  condition 
will  ever  be  attained,  for  all  gases,  so  far  as 


12  LIQUEFACTION    OF   GASES 

known,  deviate  from  this  law  before  the  tem- 
perature of  —  273°  is  reached.  The  temperature 
at  which  the  volume  of  a  perfect  gas  becomes 
equal  to  zero  (—  273°  C.  or  —460°  F.)  is  called 

the    ABSOLUTE    ZERO    OF    TEMPERATURE.         Absolute 

temperatures  are  measured  from  this  point.  The 
absolute  zero  may  also  be  defined  as  that  tem- 
perature at  which  the  kinetic  energy  of  the 
molecules  is  equal  to  zero.  Thomson  (now  Lord 
Kelvin)  has  also  proposed  a  definition  which  is 
based  entirely  upon  energy  considerations.1  This 
definition,  however,  need  not  be  discussed  here. 
He  obtained  the  value  —  273°. 7  for  the  absolute 
zero. 

Both  Dalton  and  Gay  Lussac  made  observa- 
tions on  the  change  of  temperature  which  ac- 
companies the  expansion  or  compression  of  a 
gas.  Dalton2  found  that  "about  50°  of  heat 
are  evolved  when  air  is  compressed  to  one  half 
of  its  original  volume,  and  that,  on  the  other 
hand,  50°  are  absorbed  by  the  corresponding 
rarefaction."  Gay  Lussac3  employed  two  large 
flasks,  one  of  which  contained  the  gas,  while  the 


1  Phil.  Mag.,  Oct.,  1848. 

2  Memoirs  of  the  Literary  and  Philosophical  Society  of  Man- 
chester, V,  Part  II,  pp.  251-525. 

8  See   original   memoir   in    The  Free  Expansion  of  Gases,  by 
Ames,  pp.  3-13. 


EARLY   HISTORY  13 

other  was  exhausted.  Thermometers  were  placed 
in  each  of  these  flasks,  and  the  two  were  then 
connected.  This  allowed  the  gas  to  expand  in 
one  flask,  while  it  was  being  compressed  in  the 
other.  In  this  manner,  Gay  Lussac  experimented 
with  ordinary  air,  hydrogen,  carbon  dioxide,  and 
oxygen,  and  observed  the  accompanying  changes 
of  temperature.  This  subject  has  been  more 
thoroughly  investigated  by  Joule  and  Thomson. 
Their  work  will  be  referred  to  in  a  subsequent 
chapter.  This  method,  in  recent  years,  has  be- 
come of  great  importance  in  the  production  of 
low  temperatures. 

It  has  been  considered  probable  by  some  that 
Count  Rumford,1  in  his  experiments  to  deter- 
mine the  explosive  force  of  gunpowder,  may 
have  liquefied  carbonic  acid  gas.  He  exploded 
the  powder  in  cylinders  closed  with  a  weighted, 
movable  valve.  The  following  are  his  words : 
"When  the  force  of  the  generated  elastic  vapor 
was  sufficient  to  raise  the  weight,  the  explosion 
was  attended  by  a  very  sharp  and  surprisingly 
loud  report ;  but  when  the  weight  was  not  raised, 
as  also  when  it  was  only  a  little  moved,  —  but  not 
sufficiently  for  the  elastic  vapor  to  make  its 
escape,  —  the  report  was  scarcely  audible  at  the 

1  Phil.  Trans.,  1797,  p.  222.  See  also  Alembic  Club  Reprints, 
No.  12,  p.  20, 


14  LIQUEFACTION   OF   GASES 

distance  of  a  few  paces.  ...  In  many  of  the 
experiments,  in  which  the  elastic  vapor  was 
confined,  this  feeble  report  attending  the  ex- 
plosion of  the  powder  was  immediately  followed 
by  another  noise  totally  different  from  it,  which 
appeared  to  be  occasioned  by  the  falling  back 
of  the  weight."  He  also  calls  attention  to  the 
small  degree  of  expansive  force  of  the  confined 
elastic  vapor  when  it  was  allowed  to  escape. 
Instead  of  rushing  out  with  a  loud  report,  the 
gas  escaped  with  a  hissing  noise.  The  aqueous 
vapor  produced  in  these  experiments  was  evi- 
dently condensed  to  a  liquid,  but,  in  the  light 
of  the  researches  of  Andrews,  it  seems  that  the 
temperature  produced  by  the  explosion  would 
be  higher  than  31°,  —  the  critical  temperature 
of  carbon  dioxide.  If  this  is  true,  the  carbonic 
acid,  of  course,  would  not  have  been  condensed 
to  the  liquid  state. 

In  1799  Van  Marum  1  published  an  account  of 
some  experiments  which  were  performed  several 
years  earlier.  The  main  object  of  these  observa- 
tions was  to  study  the  effect  of  low  pressures  on 
different  liquids.  Some  of  the  liquids,  he  stated, 
were  entirely  converted  to  vapors  by  this  method. 
When  the  pressure  was  increased,  these  vapors 

1  Gilbert's  Ann.,  I,  p.  145. 


EARLY   HISTORY  15 

condensed  again  to  the  liquid  state.  By  means  of 
an  air-pump,  he  compressed  ammonia  gas,  and 
found  that,  as  the  pressure  increased,  the  volume 
did  not  decrease  in  accordance  with  Boyle's  law. 
At  a  pressure  of  three  atmospheres,  he  says,  drops 
of  liquid  ammonia  were  formed.  It  is  very  proba- 
ble, however,  that  the  gas  used  in  this  experiment 
contained  a  small  quantity  of  aqueous  vapor. 

Fourcroy  and  Vanquelin  1  made  a  series  of  ex- 
periments, in  which  they  subjected  certain  gases 
to  low  temperatures.  In  Accum's  Chemistry,  I, 
P-  337>  we  nnd  the  statement  that  ammonia  gas 
was  liquefied  in  these  experiments.  It  seems,  how- 
ever, that  aqueous  ammonia  was  used  in  these  ob- 
servations, and  that  the  pure  gas  was  not  liquefied. 
These  experimenters  also  subjected  hydrochloric 
acid  gas,  sulphuretted  hydrogen,  and  sulphurous 
acid  gas  to  low  temperatures.  They  did  not  suc- 
ceed, however,  in  liquefying  any  of  these  gases. 
The  authors  state  that  they  obtained  a  temperature 
of  -  40°. 

During  this  same  year  Guyton  de  Morveau2 
experimented  with  ammonia  gas  at  low  tempera- 
tures. It  is  probable  here,  as  in  the  observations 
of  Fourcroy  and  Vanquelin,  that  the  gas  contained 
moisture.  The  method  of  drying  was  to  pass  the 

1  Ann.  de  Chim.,  29,  p.  281. 

2  Ann.  de  Chim.,  29,  pp.  290,  297. 


16  LIQUEFACTION   OF   GASES 

gas  into  a  glass  vessel,  the  temperature  of  which 
was—  21°. 25.  The  object  of  this  was  to  convert 
the  aqueous  vapor  into  ice.  From  this  balloon 
the  uncondensed  gas  passed  to  a  second  glass 
vessel,  where  it  was  subjected  to  a  temperature 
of  —43°. 25.  At  this  temperature  drops  of  liquid 
formed  on  the  interior  surfaces  of  the  containing 
vessel.  The  author  states  that  ammonia,  dried 
as  completely  as  possible  by  subjecting  to  a  tem- 
perature of —  21°,  condenses  to  a  liquid  at  —  48°. 
It  is  not  likely  that  the  gas  was  rendered  com- 
pletely dry  by  this  method ;  and  the  author  calls 
attention  to  the  fact  that  the  liquid,  produced 
at  —  48°,  probably  contained  a  small  quantity  of 
water. 

In  1805  Stromeyer  subjected  arsine  to  low  tem- 
peratures. Thenard  1  says  that  the  gas  was  con- 
densed to  a  liquid  in  these  experiments.  Another 
reference2  states  that  "Professor  Stromeyer  con- 
densed the  gas  so  far  as  to  reduce  it  in  part  to  a 
liquid,  by  immersing  it  in  a  mixture  of  snow  and 
muriate  of  lime,  in  which  several  pounds  of  quick- 
silver had  been  frozen  in  the  course  of  a  few 
minutes."  Faraday  remarks  that,  "from  the  cir- 
cumstance of  its  being  reduced  only  in  part  to  a 
liquid,  we  may  be  led  to  suspect  that  it  was  rather 

1  Traite  de  Ckimie,  I,  p.  373. 

2  Nicholson's  your.,  19,  p.  382. 


EARLY   HISTORY  17 

the  moisture  of  the  gas  that  was  condensed  than 
the  gas  itself." 

Numerous  text-books  refer  to  the  liquefaction  of 
sulphurous  acid  gas  by  Monge  and  Clouet.  Thom- 
son, in  his  System  of  Chemistry,  6th  ed.,  II,  p. 
1 1 8,  says  the  gas  was  condensed  when  exposed 
to  a  temperature  of—  18°.  In  Accum's  Chemis- 
try, I,  p.  345,  and  Murray's  Chemistry,  II,  p.  405, 
we  find  the  statement  that  the  condensation  of 
sulphurous  acid  was  effected  by  the  application  of 
strong  pressure  and  intense  cold. 

The  experiments  of  Northmore1  in  1805-1806 
are  among  the  most  important  of  the  earlier  obser- 
vations. His  object  was  to  determine  the  effect 
of  pressure  on  the  affinities  of  gases.  His  results, 
however,  show  that  some  of  the  gases  were  lique- 
fied. The  apparatus  consisted  of  an  exhausting 
syringe,  a  condensing  pump,  a  connecting  spring- 
valve,  and  glass  receivers.  When  chlorine  was 
compressed,  he  observed  the  formation  of  a  yel- 
low, extremely  volatile,  fluid.  This  appears  to  be 
the  first  reliable  account  of  the  liquefaction  of 
chlorine.  He  also  liquefied  hydrochloric  acid  gas 
and  sulphurous  acid  gas.  The  latter  experiment, 
he  says,  corroborates  the  statement  of  Monge  and 
Clouet,  that  sulphurous  acid  is  condensed  to  a 

1  Nicholson's  Jour.,  12.  p.  368,  and  13,  p.  233.  Also  Alembic 
Club  Reprints,  No.  12,  pp.  69-79. 


i8  LIQUEFACTION   OF   GASES 

liquid  by  the  simultaneous  application  of  strong 
pressure  and  low  temperature.  In  the  experi- 
ments on  carbonic  acid,  Northmore  remarks  that 
the  receiver  very  unexpectedly  bursts  with  violence. 

These  observations  were  very  successful,  consid- 
ering the  period  in  which  they  were  made.  It  is 
difficult  to  understand  why  the  results  obtained  by 
Northmore  were  no  incentive  to  further  investi- 
gation. The  fact  remains,  however,  and  these 
experiments  have  only  an  historical  interest. 

In  1822,  Cagnaird  de  la  Tour1  made  a  rather 
extended  series  of  experiments  by  heating  liquids 
in  sealed  glass  tubes.  This  work  is  of  considera- 
ble importance,  in  as  much  as  it  is  a  forerunner 
of  the  researches  of  Andrews  on  critical  constants. 
Tour  called  attention  to  the  following  facts  :  — 

1.  Alcohol,  naphtha,  and  ether,  when  subjected 
to  heat  and  pressure,  are  converted  into  vapors  in 
a  space  slightly  greater  than  double  that  of  each 
liquid. 

2.  The  increased  pressure,  due  to  the  presence 
of  air  in  the  tube,  did  not  prevent  the  evaporation 
of  the  liquid  in  the  same  space.     The  expansion, 
however,  was  more  regular. 

3.  The  experiments  on  water  were  unsatisfac- 
tory, owing  to  imperfections  in  the  apparatus. 

1  Ann.  de  Chim.  et  de  Phys.,  21,  pp.  127,  178. 


EARLY    HISTORY 


Ether  is  completely  vaporized  in  a  space  some- 
what less  than  double  that  of  the  liquid,  at  a  tem- 
perature of  about  1 60°.  The  pressure  exerted  by 
ether  at  this  temperature  is  from  37  to  38  atmos- 
pheres. At  a  temperature  of  200°,  alcohol  vaporizes 
in  a  space  less  than  three  times  that  of  the  liquid^. 
The  pressure  in  this  case  is  about  1 19  atmospheres. 

The  measurements  on  ether  are  given  in  the 
following  tables  : l  — 


Volume  of  Liquid  =  7                                  Volume  of  Vapor  =  20 

Temperature  in 
Reaumur  Degrees 

Pressures  in  Atmos- 
pheres 

Differences 

80° 

5 

—            —  ««* 

90 

7 

2 

100 

10 

3 

110 

12 

2 

120 

18 

6 

I30 
140 

22 
28 

4 
6 

State  of  Vapor  I  50 
1  60 

37 

48 

9 
ii 

170 
1  80 
IQO 
200 

59 
68 

78 
86 

ii 
9 

10 

8 

260 

130 

— 

1  Ann.  de  Chim.  et  de  Phys.,  22,  pp.  411,  412. 


20 


LIQUEFACTION   OF   GASES 


The  results  obtained  by  heating  one  half  of  this 
quantity  of  liquid  in  a  tube  of  the  same  volume 
were  as  follows  :  — 


Volume  of  Liquid  =  35                               Volume  of  Vapor  =  20 

Temperature  in 
Reaumur  Degrees 

Pressures  in  Atmos- 
pheres 

Differences 

100° 

14 

— 

no 

17 

3 

120 

22 

5 

I30 

28 

6 

I4O 

35 

7 

State  of  Vapor    1  50 

42 

7 

1  60 

5° 

8 

170 

58 

8 

1  80 

63 

5 

I90 

66 

3 

200 

70 

4 



— 

4 



— 

4 



— 

3 

260 

94 

4 

The  important  part  of  these  observations  is, 
that  the  liquid  disappeared  at  the  same  tempera- 
ture in  both  cases.  This  was  an  indication  that, 
regardless  of  the  pressure,  the  substance  cannot 
exist  in  the  liquid  state  when  heated  above  a  cer- 
tain temperature.  These  results  exerted  but  little 
influence  until  after  the  work  of  Andrews  nearly 
fifty  years  later. 


EARLY   HISTORY  21 

So  far  the  investigations  are  only  of  historical 
interest.  The  results  which  are  recorded  on  the 
preceding  pages  have  been  of  little  value  to  the 
later  experimenters.  From  this  point  the  work 
becomes  more  systematic.  The  interesting  obser- 
vations of  Cagnaird  de  la  Tour  may  be  said  to 
close  the  first  chapter  in  the  liquefaction  of  gases. 


CHAPTER   II 

HERE,  as  in  many  other  lines  of  scientific  re- 
search, we  must  turn  to  Faraday  for  the  first  sys- 
tematic observations.  This  great  experimenter  has 
taken  the  initiative  step  in  many  lines  of  scientific 
investigation,  and  is  the  author  of  numerous  and 
important  discoveries.  In  1823,  Faraday  acci- 
dentally liquefied  chlorine.  Although  an  accident, 
he  perceived  the  full  significance  of  the  result, 
and  followed  the  observation  with  two  elaborate 
series  of  experiments,  in  which  he  exhausted  all 
his  resources  in  the  endeavor  to  liquefy  the  so- 
called  permanent  gases. 

At  the  suggestion  of  Davy,  Faraday  experi- 
mented with  the  hydrate  of  chlorine  and  studied 
the  effect  of  heating  it  in  a  closed  glass  tube. 
When  placed  in  water  at  60°,  he  observed  no 
change;  but  when  placed  in  water  at  100°,  a  yel- 
low gas  was  set  free.  On  cooling,  this  gas  con- 
densed to  a  yellow  liquid  which  resembled  the 
chloride  of  nitrogen.  During  the  progress  of  this 
experiment,  Dr.  Paris1  happened  to  enter  the  lab- 

1  Tyndall,  Faraday  as  a  Discoverer,  p.  14. 
22 


EXPERIMENTS    OF   FARADAY  23 

oratory.  "  Seeing  the  oily  liquid  in  the  tube,  he 
rallied  the  young  chemist  for  his  carelessness  in 
employing  soiled  vessels.  .  .  .  Early  the  next  morn- 
ing, Dr.  Paris  received  the  following  note  :  — 

" '  DEAR  SIR,  —  The  oil  you  noticed  yesterday  turns  out 
to  be  liquid  chlorine. 

" '  Yours  faithfully, 

<"M.  FARADAY.'" 

The  chlorine  had  been  liquefied  by  pressure. 
When  the  tube  was  opened,  the  contents  ex- 
ploded. 

Faraday  made  a  number  of  observations  to 
prove  that  this  yellow  liquid  was  chlorine. 
Among  other  experiments,  he  subjected  dry 
chlorine  gas  to  pressure,  and  obtained  a  liquid 
which  was  similar  in  all  respects  to  that  obtained 
from  the  hydrate.  He  also  made  some  ap- 
proximate determinations  of  the  density  of  liquid 
chlorine. 

Almost  simultaneous  with  this  work  of  Fara- 
day, Davy1  liquefied  hydrochloric  acid  gas  by 
treating  ammonium  chloride  with  sulphuric  acid 
in  a  closed  tube.  He  then  substituted  ammonium 
carbonate  for  the  chloride,  and  endeavored  to 
liquefy  carbon  dioxide.  Only  one  experiment  was 

1  Note  to  Faraday's  article  on  "  Liquefaction  of  Chlorine." 


24  LIQUEFACTION   OF   GASES 

made,  and,  in  that  case,  the  tube  burst.  At  the 
suggestion  of  Davy,  Faraday  continued  the  work 
alone. 

In  these  experiments,  a  number  of  gases  were 
subjected  to  pressure,  and  the  results  were  pub- 
lished in  one  article1  in  1823. 

Sulphurous  Acid 

Mercury  and  concentrated  sulphuric  acid  were 
placed  in  a  closed,  bent  glass  tube  which  was 
afterward  sealed  (Fig.  i).  The  end  of  the  tube 

containing  the  reacting 
substances  was  heated, 
while  the  other  end  was 
kept  cool  by  means  of 
moistened  paper.  Sul- 
phurous acid  gas  was  gen- 
erated, and,  after  the 
FIG.  i. 

sulphuric  acid  had  become 

saturated,  it  was  evolved,  and  condensed  to  a  liquid 
in  the  cold  end  of  the  tube.  Faraday  remarks 
that  sulphurous  acid  forms  a  limpid,  colorless, 
highly  fluid  liquid,  which  does  not  solidify  at  o°  F. 
When  the  tube  was  opened,  a  portion  of*  the  liquid 
evaporated  rapidly.  This  lowered  the  tempera- 

1  Phil.  Trans.,  113,  pp.  189-198.  See  also  Akmbic  Club 
Reprints,  No.  12,  pp.  10-19. 


EXPERIMENTS    OF   FARADAY  25 

ture  of  the  remaining  portion,  so  that  it  re- 
mained a  liquid  'for  some  time  at  the  ordinary 
atmospheric  pressure.  A  piece  of  ice  thrown 
into  the  liquid  caused  rapid  boiling.  Faraday 
then  took  dry  sulphurous  acid  gas,  and  subjected 
it  to  pressure  in  a  glass  tube  by  means  of  a 
syringe.  When  the  tube  was  cooled  to  o°  F.,  the 
gas  condensed  to  a  liquid  which  was  similar  to 
that  obtained  from  the  mercury  and  sulphuric  acid. 

Sulphuretted  Hydrogen 

In  this  experiment  the  sealed  glass  tube  con- 
tained hydrochloric  acid  and  sulphuret  of  iron. 
On  warming  the  contents,  sulphuretted  hydrogen 
was  generated  and  condensed  in  the  longer  end 
of  the  tube,  which  was  surrounded  by  a  mixture  of 
ice  and  salt.  The  resulting  liquid  was  colorless, 
limpid,  and  excessively  fluid.  By  the  introduction 
of  a  small  gauge  intOj  the  tube,  he  found  the  pres- 
sure to  be  nearly  17  atmospheres  at  the  tempera- 
ture of  50°  F. 

Carbonic  Acid 

The  materials  used  in  this  case  were  ammonium 
carbonate  and  concentrated  sulphuric  acid.  The 
glass  tubes,  however,  were  much  stronger  than 
those  used  in  the  previous  experiments.  Even 
then  a  number  of  violent  explosions  resulted. 


26  LIQUEFACTIOiN    OF   GASES 

The  carbonic  acid  was  condensed  to  a  color- 
less, extremely  fluid  liquid.  The  vapor  pressure 
at  32°  F.  was  measured,  and  found  to  be  36 
atmospheres. 

Euchlorine 

This  gas  was  generated  from  a  mixture  of  potas- 
sium chlorate  and  sulphuric  acid  in  a  closed  tube. 
On  cooling,  it  condensed  to  a  yellow,  transparent 
liquid. 

Nitrous  Oxide 

Ammonium  nitrate,  dried  by  heating  in  the  air  to 
partial  decomposition,  was  heated  in  a  closed  bent 
tube.  When  the  gases  were  cooled,  two  liquids 
separated.  One  was  found  to  be  water  containing 
a  little  nitrous  oxide  in  solution,  while  the  other 
was  nitrous  oxide.  The  appearance  of  the  liquid 
was  similar  to  that  of  carbonic  acid.  The  vapor 
pressure  at  45°  F.  was  foundtto  be  50  atmospheres. 
These  experiments  were  accompanied  by  a  number 
of  violent  explosions. 

Cyanogen 

Pure,  dry,  mercuric  cyanide  was  treated  in  a 
manner  similar  to  that  of  ammonium  nitrate.  The 
resulting  cyanogen  was  condensed  in  the  cold 
end  of  the  tube  to  a  limpid,  colorless,  liquid. 


EXPERIMENTS   OF   PERKINS  27 

The  vapor  pressure   at  45°  F.   was  found   to  be 
3.6  atmospheres. 

Ammonia 

Dry  silver  chloride  was  allowed  to  absorb  pure, 
dry  ammonia  gas.  The  substance  was  then  heated 
in  a  closed  tube.  The  gas  was  again  set  free,  and 
was  condensed  to  a  colorless,  transparent  liquid  in 
the  longer  arm  of  the  tube,  which  was  cooled  by 
means  of  ice  and  water.  The  vapor  pressure  at 
50°  F.  was  about  6.5  atmospheres. 

Faraday  repeated  the  experiments  of  Davy  on 
hydrochloric  acid.  He  also  determined  a  number 
of  physical  constants  of  these  various  liquids.  He 
attempted  to  liquefy  hydrogen,  oxygen,  etc.,  but 
without  success.  Twenty-one  years  later,  he  pub- 
lished another  series  of  experiments  on  the  lique- 
faction of  gases.  These  observations  will  be 
considered  in  their  proper  place.  Meanwhile  we 
may  turn  our  attention  to  the  work  of  other 
investigators. 

EXPERIMENTS  OF  PERKINS 

In  a  note,1  published  in  1823,  Perkins  calls 
attention  to  a  series  of  experiments  on  compressed 
air.  The  details  of  the  work  were  not  published 
until  a  few  years  later.  The  primary  object  of  the 

1  Annals  of  Phil,  VI,  p.  66. 


28  LIQUEFACTION   OF   GASES 

investigation  was  to  study  the  effect  of  high  press- 
ure on  liquids.  The  author  states,  however,  that 
when  ordinary  air  was  subjected  to  a  pressure  of 
1000  atmospheres,  drops  of  liquid  began  to  form, 
and  that  at  1200  atmospheres,  a  beautiful  trans- 
parent liquid  could  be  seen  on  the  surface  of  the 
mercury.  The  liquid  remained  in  the  tube  after 
the  pressure  had  been  removed.  Perkins  sup- 
posed that  the  liquid  thus  formed  was  condensed 
air.  From  the  researches  of  later  experimenters, 
however,  it  is  evident  that  ordinary  air  cannot  be 
liquefied  under  such  conditions.  The  liquid  which 
appeared  at  the  surface  of  the  mercury  was  evi- 
dently formed  by  the  condensation  of  aqueous 
vapor.  Perkins  also  remarks  that  he  liquefied  car- 
buretted  hydrogen  at  a  pressure  of  1200  atmos- 
pheres. He  developed  a  method  for  obtaining 
extremely  high  pressures. 

/ 

EXPERIMENTS  OF  BUSSY 

In  1824,  Bussy1  published  a  series  of  observa- 
tions on  the  liquefaction  of  gases.  His  method  of 
procedure  was  entirely  different  from  that  of  Fara- 
day. He  subjected  the  gases  to  low  temperatures, 
but  did  not  increase  the  pressure.  He  condensed 

1  Ann.  de  Ckim.  et  de  Phys.,  XXVI,  p.  63;  Pogg.  Ann.,  I,  p.  237, 
1824. 


EXPERIMENTS   OF   BUSSY  29 

sulphurous  acid  to  a  colorless,  transparent  liquid, 
at  the  ordinary  atmospheric  pressure,  by  subject- 
ing it  to  a  temperature  of  — 18  to  —20°.  Bussy 
observed  that  if  the  liquid  sulphurous  acid  was 
allowed  to  evaporate  in  the  air,  the  temperature 
sank  to  -  57°,  and  that  if  evaporated  under 
reduced  pressure,  the  temperature  sank  to  —65°. 
His  work  was  a  great  advance  in  the  liquefaction 
of  gases,  inasmuch  as  he  made  use  of  this  method 
to  produce  low  temperatures.  By  means  of  liquid 
sulphurous  acid,  he  liquefied  chlorine  and  ammo- 
nia, and  in  a  similar  manner  he  liquefied  and 
solidified  cyanogen.  This  method  of  lowering  the 
temperature  soon  came  into  general  use  for  both 
scientific  and  industrial  purposes.^ 

Heat  of  Vaporization 

Inasmuch  as  the  evaporation  of  liquids  becomes, 
at  this  period,  an  important  method  for  the  pro- 
duction of  low  temperatures,  we  may  briefly  con- 
sider, at  this  point,  the  -thermal  change  which 
accompanies  the  passage  of  a  substance  from  the 
liquid  to  the  gaseous  state. 

When  a  liquid  changes  to  the  gaseous  state,  a 
certain  quantity  of  heat  is  absorbed.  The  heat 
required  to  change  one  gram  of  a  liquid  to  a 
vapor,  at  the  same  temperature  and  pressure,  is 


30  LIQUEFACTION   OF   GASES 

called  the  heat  of  vaporization.    The  heat  absorbed 
is  used  :  — 

1.  To  increase  the  internal  energy  of  the  sub- 
stance ;   i.e.  the  energy  of  the  particles   must  be 
sufficiently   increased    to   overcome   the   force   of 
cohesion. 

2.  To  perform  external  work  ;  i.e.  the  volume  of 
the  substance  must  be  increased  against  a  definite 
pressure. 

Let  E  represent  the  energy  of  the  vapor,  and  E± 
the  energy  of  the  liquid,  then  the  increase  in  the 
internal  energy  is 

E-EX 

If  Fand  V\  represent  the  volumes  of  the  vapor 
and  liquid,  and  p  is  the  pressure,  which  remains 
constant,  then  the  external  work  performed  is 
equal  to 

P(V-VI). 

The  total  energy  and  work  required  to  vaporize  a 
liquid,  therefore,  is 


Knowing  the  mechanical  equivalent  of  heat,  this 
expression  may  be  represented  in  thermal  units  ; 
in  this  latter  form  it  represents  the  heat  of  vapori- 
zation. The  numerical  value  of  the  heat  of  vapori- 
zation depends  upon  the  temperature. 

Inasmuch  as  heat  is  absorbed  during  evaporation, 


EXPERIMENTS   OF   COLLADON  31 

it  is  evident  that  a  liquid  cannot  maintain  a  con- 
stant temperature  during  the  process  of  evapora- 
tion, unless  it  receives  heat  from  some  external 
source.  Ordinarily,  there  is  a  constant  flow  of 
heat  from  the  surrounding  bodies  to  the  liquid 
during  evaporation. 

Suppose,  however,  that  this  supply  of  heat  from 
the  surrounding  bodies  is  cut  off  by  insulation,  then 
the  heat  required  in  the  evaporation  must  be  drawn 
from  the  liquid  itself.  The  temperature,  of  course, 
will  be  lowered  by  this  process.  If  the  evapora- 
tion be  hastened,  e.g.  by  reducing  the  pressure,  the 
temperature  will  be  reduced  more  rapidly  and  to 
a  much  greater  degree.  Leslie  has  shown  that 
water  can  be  frozen  by  means  of  its  own  evapora- 
tion under  reduced  pressure. 

EXPERIMENTS  OF  COLLADON 

In  1828  Colladon  1  constructed  an  apparatus 
for  the  purpose  of  liquefying  ordinary  air.  The 
general  plan  of  the  apparatus  is  shown  in  figure  2. 

The  pressure  was  produced  by  means  of  an 
hydraulic  pump,  and  transmitted  through  the  tube 
Cc  to  the  interior  of  a  strong  steel  cylinder  B, 
which  was  partially  filled  with  mercury.  In  this 
cylinder  was  placed  a  glass  tube  T  which  was 

1  Pictet,  Ann.  de  Chim.  et  de  Phys.  [5],  XIII,  p.  226. 


LIQUEFACTION   OF   GASES 


open    at    the 
lower  end,  but 
fused    at    the 
upper  end  to 
the         thick- 
walled,  closed 
glass    tube    /, 
the       interior 
diameter      of 
which  was  from  1.5 
to  2  mm.    This  tube 
t  projected  from  the 
cylinder  through  the 
elongated  cover  A, 
above  which  it  was 
bent    downward    to 
as  shown  in  the 
figure.      The    bent- 
down  portion  of  the 
tube  was  placed  in 
a  freezing  mixture. 
In  case  of  condensation  the 
liquid,  of  course,  would  col- 
lect in  the  lower  end  of  the 
tube  /'. 

Colladon  experimented  at 
a  temperature  of  —30°  and 
with  pressures  as  high  as 


FIG.  3. 


EXPERIMENTS   OF   THILORIER 


33 


400  atmospheres.     The  results,  however,  were  all 
negative. 

EXPERIMENTS  OF  THILORIER 

In  1834  Thilorier  l  liquefied  carbonic  acid  on  a 
much   larger  scale  than  had  hitherto  been  done. 

r\ 


T 


MG.  3. 

The  general  plan  of  the  apparatus2  employed  is 
shown  in  figures  3  and  4.      The  gas  is  generated 

1  Ulnstitut,  58,  p.  197 ;  Ann.  de  Chim.  et  ae  Phys.,  60,  pp.  427, 432. 

2  Lieb.  Ann.,  30,  p.  122. 

D 


34  LIQUEFACTION   OF   GASES 

in  the  wrought-iron  vessel  A,  and  compressed  by 
means  of  its  own  pressure  in  the  wrought-iron  re- 
ceiver F.  These  two  vessels  are  similarly  con- 
structed. B  represents  a  cross-section  of  the 
cylinder  A.  This  vessel  is  supported  by  means 
of  two  pivots  so  that  it  can  be  rotated.  Eighteen 
hundred  grams  of  bicarbonate  of  sodium,  and  4^ 
litres  of  water  are  placed  in  the  generator.  The 
vessel  D  is  then  filled  with  concentrated  sulphuric 
acid,  and  placed  in  the  cylinder  with  the  sodium 
bicarbonate  and  water.  The  stopper  c  is  then 
screwed  tightly  into  the  top  of  the  generator,  and 
connection  made  with  the  receiver  by  means  of 
the  copper  tube  E.  On  rotating  the  vessel  A,  the 
sulphuric  acid  in  D  comes  in  contact  with  the  car- 
bonate. The  carbonic  acid  gas  which  is  evolved 
in  the  reaction  produces  a  very  high  pressure  in 
the  generator.  After  several  minutes  the  stop- 
cocks mm  are  opened.  The  gas  rushes  immedi- 
ately into  the  receiver  until  the  pressures  in  the 
two  vessels  are  equal.  A  portion  of  the  gas  is 
liquefied  by  pressure.  The  quantity  of  liquid  pro- 
duced may  be  largely  increased  by  surrounding 
the  receiver  with  a  freezing  mixture.  When  equi- 
librium has  been  established  between  the  two  ves- 
sels A  and  Fy  the  stop-cocks  ;;/  and  m  are  closed. 
The  pressure  in  the  generator  is  then  relieved,  the 
contents  are  removed,  and  a  new  charge  is  intro- 


EXPERIMENTS   OF   THILORIER 


35 


duced.     The   process  is  repeated  in  this  manner 
until  from  2  to  3  litres  of  liquid  carbonic  acid  have 


FIG.  4. 

collected  in  the  receiver.     From  five  to  ten  repeti- 
tions are  usually  required. 

In  this  way,  Thilorier  obtained  liquid  carbonic 


36  LIQUEFACTION   OF  GASES 

acid  in  rather  large  quantities,  and  made  a  series 
of  observations  on  its  physical  properties.  He 
measured  the  vapor  pressure  at  different  temper- 
atures and  found  it  to  be  36  atmospheres  at  o°, 
and  73  atmospheres  at  30°.  He  also  determined 
the  specific  gravity,  and  made  observations  on  the 
thermoscopic  effect  of  the  liquid.  The  condensed 
gas  was  found  to  be  insoluble  in  water  and  fat 
oils,  but  soluble  in  all  proportions  in  alcohol,  ether, 
naphtha,  turpentine,  and  carbon  disulphide.  It 
reacts  with  metallic  potassium,  but  produces  no 
effect  on  lead,  tin,  copper,  iron,  etc.  The  abnor- 
mal expansion  of  the  liquid  carbonic  acid  was  also 
investigated. 

Thilorier  made  some  important  observations  on 
the  production  of  low  temperatures  by  the  evapo- 
ration of  liquid  carbonic  acid.  When  a  jet  of  the 
liquid  was  directed  upon  the  bulb  of  an  alcohol  ther- 
mometer, the  temperature  sank  rapidly  to  —90°. 
The  sphere  of  action,  however,  in  this  as  well  as 
in  other  cases  was  limited  almost  entirely  to  the 
point  of  contact.  The  congelation  of  mercury  was 
confined  to  small  portions  of  it ;  and  when  the 
hand  was  exposed  to  a  jet  of  the  liquid,  a  burning 
sensation  was  felt,  but  the  effect  was  confined  to 
very  narrow  limits. 

The  author  explained  this  limited  sphere  of 
action  by  the  low  conductivity  and  small  capacity 


EXPERIMENTS   OF   THILORIER  37 

for  heat  of  carbonic  acid.  He  says :  "  If  gases 
have  little  effect  in  the  production  of  cold,  it  is  not 
so  with  vapors  whose  conductivity  and  capacity  for 
heat  are  much  greater.  I  have,  therefore,  thought 
that  if  a  permanent  liquid  —  ether,  for  example  — 
could  be  placed  under  the  same  conditions  of 
expansibility  as  liquefied  gases,  we  might  obtain 
a  frigorific  effect  much  greater  than  that  produced 
by  liquid  carbonic  acid.  To  accomplish  this,  ether 
must  be  rendered  explosible,  and  this  I  have  easily 
effected  by  mixing  it  with  liquid  carbonic  acid. 
In  this  intimate  combination  of  the  two  liquids, 
which  dissolve  each  other  in  all  proportions,  ether 
ceases  to  be  a  permanent  liquid  at  the  ordinary 
atmospheric  pressure ;  it  becomes  expansible  like 
a  condensed  gas,  still  preserving  its  properties  of 
a  vapor;  namely,  its  conductivity  and  capacity 
for  heat." 

The  effects  of  a  jet  of  explosible  ether  are  more 
pronounced  and  extend  over  a  much  greater  area 
than  those  produced  by  a  jet  of  liquid  carbonic 
acid.  Fifty  grams  of  mercury  can  be  solidified  in 
a  few  seconds  by  means  of  this  mixture. 

Solidification  of  Carbonic  Acid 

Thilorier  not  only  liquefied  carbonic  acid,  but 
succeeded  in  converting  it  into  a  solid.  The 


LIQUEFACTION   OF   GASES 


receiver  which  contained  the  liquid  carbonic  acid 
was  connected  with  a  vessel  formed  of  two  sepa- 
rate halves  (Fig.  5)  by  means  of  a  small  tube. 
The  sudden  expansion  produced  a  very  low  tem- 
perature, and  a  portion  of  the  gas  solidified.  The 
author  thought,  however,  that  the  solid  particles 
were  composed  of  ordinary  ice  which  resulted  from 
the  freezing  of  aqueous  vapor  in  the  air.  The 
experiment  was  repeated  before  Arago,  Thenard, 


\ 


FIG.  5. 


and  Dulong.  The  solid  portions  were  then  found 
to  be  carbonic  acid.  "  Gaseous  at  the  ordinary 
temperature  and  pressure,  and  liquid  at  o°  under  a 
pressure  of  36  atmospheres,  carbonic  acid  becomes 
solid  at  a  temperature  of  about  100°  below  zero, 
and  retains  this  new  condition  for  several  minutes 
in  the  open  air,  without  the  necessity  of  any  com- 
pression." 

The  author  calls  attention  also  to  the  remarkable 
difference  in  the  behavior  of  the  liquid  and  solid 


EXPERIMENTS   OF  ADDAMS  39 

acid.  While  in  the  liquid  state,  he  says,  the 
elastic  force  is  exceedingly  great,  —  being  equal 
in  explosive  power  to  an  equal  weight  of  gun- 
powder. The  solid,  on  the  other  hand,  disappears 
insensibly  by  slow  evaporation.  A  fragment  of 
solid  carbonic  acid,  he  adds,  slightly  touched  by 
the  ringer,  glides  rapidly  over  a  polished  surface, 
as  if  sustained  by  the  gaseous  atmosphere  with 
which  it  is  constantly  surrounded,  until  it  is  entirely 
dissipated.  The  vaporization  of  solid  carbonic 
acid  is  complete.  It  leaves  but  rarely  a  slight 
humidity,  which  may  be  attributed  to  the  action  of 
the  air  on  a  cold  body,  the  temperature  of  which 
is  far  below  that  of  freezing  mercury. 

The  solidification  of  large  quantities  of  carbonic 
acid  has  been  of  great  value  to  later  experimenters 
for  the  production  of  low  temperatures.  The  solid 
acid  moistened  with  ordinary  ether  is  known  as 
Thilorier's  Mixture.  A  temperature  of 

-110°=-  i66°F. 
can  be  obtained  by  means  of  this  mixture. 

Modification  of  Thilorier's  Apparatus 

In  a  paper  read  before  the  British  Association 
for  the  Advancement  of  Science,1  Addams  calls 
attention  to  three  forms  of  apparatus  which  had 

1  Proceedings  for  1838,  p.  70. 


40  LIQUEFACTION   OF   GASES 

been  used  by  him  to  liquefy  and  solidify  carbonic 
acid  on  a  large  scale.  The  first  method  is  me- 
chanical, in  which  powerful  hydraulic  pumps  are 
used  to  force  the  gas  from  one  vessel  into  a 
second,  by  filling  the  first  with  water,  saline  solu- 
tions, oil,  or  mercury.  The  second  form  of  appa- 
ratus is  a  modification  of  that  invented  and  used 
by  Thilorier.  The  third  includes  the  mechanical 
and  the  chemical  methods,  by  means  of  which 
much  of  the  acid  formed  in  the  generator  is  pre- 
served ;  whereas  by  the  arrangement  of  Thilorier, 
two  parts  in  three  rush  into  the  atmosphere  and 
are  lost.  The  apparatus  is  provided  with  two 
gauges,  —  one  to  determine  when  the  generator  is 
filled  with  water,  and  the  other  to  indicate  the 
quantity  of  liquid  acid  in  the  receiver.  By  means 
of  this  apparatus,  Addams  prepared  liquid  carbonic 
acid  in  considerable  quantity  and  measured  the 
elastic  force  at  different  temperatures.  The  solid 
carbonic  acid  used  by  Faraday  in  his  second  series 
of  experiments  on  the  liquefaction  of  gases  was 
prepared  by  Addams. 

EXPERIMENTS  ON  HYDROGEN  AND  OXYGEN 

In  these  experiments  Maugham a  attempted  to 
liquefy  hydrogen  and  oxygen  by  means  of  press- 

1  Proc.  Brit.  Assoc.for  Adv.  of  Sci.  (1838),  p.  73. 


EXPERIMENTS   OF   TORREY  41 

ure.  The  pressure  was  obtained  by  the  elec- 
trolysis of  acidulated  water  in  closed,  strong  glass 
U-tubes.  In  this  manner,  the  author  was  able  to 
burst  tubes  of  the  strongest  glass.  He  suggested 
that  if  the  experiments  were  carried  out  at  low 
temperatures,  the  hydrogen  and  oxygen  would 
probably  condense  to  the  liquid  state.  This 
method  for  obtaining  high  pressures  has  been  used 
by  some  of  the  later  experimenters. 
• 

OBSERVATIONS  OF  TORREY 

These  experiments  were  not  published  by  the 
author,  but  the  results  were  communicated  in 
private  letters  to  Dr.  Silliman,  who  published  them 
two  years  later.1  The  editors  make  the  following 
statement :  — 

"  We  have  been,  from  time  to  time,  informed  by 
letters  from  Prof.  John  Torrey  of  New  York,  of 
his  progress  in  the  condensation  of  gases,  and 
although  not  intended  for  publication,  we  now 
take  the  liberty  to  give  some  citations  from  his 
letters." 

April  11,  1837,  Torrey  writes  that,  although 
he  was  unable  to  procure  a  suitable  form  of 
apparatus  in  which  to  condense  carbonic  acid,  he 
had  successfully  carried  out  numerous  experiments 

1  Silliman'1  s  Jour.,  35,  p.  374,  1839. 


42  LIQUEFACTION   OF   GASES 

with  glass  tubes.  A  month  later  he  forwarded  a 
tube  containing  liquid  carbonic  acid  to  Dr.  Silli- 
man.  Torrey  also  liquefied  sulphurous  acid  and 
chlorochromic  acid.  Perfectly  dry  phosphorus, 
he  says,  is  not  inflamed  by  liquid  chlorochromic 
acid,  but  if  moist  in  the  slightest  degree,  it  will 
burn  with  a  loud  explosion,  requiring  particular 
precautions.  In  another  letter,  he  remarks,  "  I 
have  been  shooting  with  an  air-gun,  using  liquid 
carbonic  acid  for  throwing  the  balls,  and  I  hope 
soon  to  emulate  Perkins'  steam  gun." 

EXPERIMENTS  OF  MITCHELL 

In  1839  Mitchell1  modified  the  apparatus  of 
Thilorier  somewhat,  and  obtained  both  liquid  and 
solid  carbonic  acid.  When  the  liquefied  gas  is 
allowed  to  escape  into  an  iron  receiver,  he  says, 
"  a  large  portion  of  the  liquid  is  instantly  expanded 
into  gas  which  escapes  through  a  tube.  The 
coldness  consequent  on  the  enormous  expansion 
freezes  another  portion  of  the  liquid,  which  then 
falls  to  the  bottom  of  the  receiver.  About  one 
drachm  of  solid  matter  is  thus  formed  for  each 
ounce  of  liquid." 

Mitchell  also  made  a  series  of  observations  on 
the  physical  constants  of  liquid  and  solid  carbonic 

1  Sillimatfs  Jour.,  35,  p.  346. 


EXPERIMENTS   OF   AIME  43 

acid.  By  means  of  the  solid  acid  he  solidified 
mercury,  and  experimented  with  the  solid  metal. 
Liquid  sulphurous  acid  freezes  at  about  —80°, 
while  ordinary  ether,  he  says,  when  subjected  to 
a  temperature  of  — 100°  is  not,  in  the  slightest 
degree,  altered.  He  further  adds  that,  "when  a 
piece  of  solid  carbonic  acid  is  pressed  against  a 
living  animal  surface,  it  drives  off  the  circulating 
fluids,  and  produces  a  ghastly  white  spot.  If  held 
for  fifteen  seconds  it  raises  a  blister,  and  if  the 
application  be  continued  for  two  minutes,  a  deep 
white  depression  with  an  elevated  margin  is  per- 
ceived ;  the  part  is  killed,  and  a  slough  is  in  time 
the  consequence.  I  have  thus  produced  both 
blisters  and  sloughs,  by  means  nearly  as  prompt 
as  fire,  but  much  less  alarming  to  my  patients." 
Experiments  were  also  made  with  a  number  of 
liquids  and  metals,  by  placing  them  in  liquid 
carbonic  acid. 

EXPERIMENTS  OF  AIME  (I843)1 

In  these  experiments,  ethylene,  nitric  oxide, 
nitrogen,  hydrogen,  carbon  monoxide,  and  oxygen 
were  subjected  to  very  high  pressures.  The  press- 
ure was  obtained  by  sinking  the  gases  in  suitable 
vessels  to  great  depths  in  the  ocean.  The  method, 

1  Ann.  de  Chim.  et  de  P/iys.,  8,  p.  275,  1843. 


44 


LIQUEFACTION   OF   GASES 


of  course,  is  unsatisfactory,  inasmuch  as  the  obser- 
vations cannot  be  made  at  the  time  when  the 
pressure  is  applied. 

The  following  table  will  show  the  relative  de- 
crease in  volume  for  the  different  gases  when 
subjected  to  pressure  :  — 


Substance 

Pressure 

Ratio  of  Original  Volume 
to  Final  Volume 

Oxygen 

83  atmospheres 

90: 

Ethvlene 

124           « 

356: 

Nitric  oxide 

165 

251: 

Carbon  monoxide 

165 

180: 

Oxygen 

165           « 

160: 

Fluosilicon 

105            " 

350: 

Aime  thought  that  the  ethylene  and  fluosilicon 
were  condensed  to  the  liquid  state.  The  evi- 
dence, however,  is  not  conclusive.  Hydrogen  and 
nitrogen  were  subjected  to  a  pressure  of  220 
atmospheres,  without  showing  any  indications  of 
liquefaction.  The  observations  seem  to  show  de- 
viations from  Boyle's  law,  but  the  results  obtained 
for  oxygen  are  somewhat  contradictory. 

EXPERIMENTS  OF  FARADAY 

In  1845  Faraday1  published  a  second  series  of 
observations.  In  the  introduction,  he  says:  "The 


1  Phil.  Trans.,  135,  p.  155;   also,  Alembic  Club  Reprints,  No.  12, 
P- 33- 


EXPERIMENTS   OF   FARADAY  45 

experiments  formerly  made  on  the  liquefaction  of 
gases,  and  the  results  which  from  time  to  time 
have  been  added  to  this  branch  of  knowledge, 
especially  by  Thilorier,  have  left  a  constant  de- 
sire on  my  mind  to  renew  the  investigation.  This, 
with  considerations  arising  out  of  the  apparent 
simplicity  and  unity  of  the  molecular  constitution 
of  all  bodies  when  in  the  gaseous  or  vaporous  state, 
which  may  be  expected,  according  to  the  indica- 
tions given  by  the  experiments  of  Cagnaird  de  la 
Tour,  to  pass  by  some  simple  law  into  the  liquid 
state,  and  also  the  hope  of  seeing  nitrogen,  oxy- 
gen, and  hydrogen,  either  as  liquid  or  solid  bodies, 
and  the  latter  probably  as  metal,  have  lately  in- 
duced me  to  make  many  experiments  on  the  sub- 
ject." 

The  gases,  in  these  experiments,  were  subjected 
to  the  simultaneous  influence  of  high  pressure  and 
low  temperature.  The  pressure  was  obtained  by 
the  use  of  two  air-pumps.  "The  first  pump  had 
a  piston  of  an  inch  in  diameter,  and  the  second 
a  piston  of  only  half  an  inch  in  diameter,  and 
these  were  so  associated  by  a  connecting  pipe, 
that  the  first  pump  forced  the  gas  into  and  through 
the  valves  of  the  second,  and  then  the  second 
could  be  employed  to  throw  forward  this  gas, 
already  compressed  to  10,  15,  or  20  atmospheres, 
into  its  final  recipient  at  a  much  higher  pressure." 


46  LIQUEFACTION   OF   GASES 

The  pressure  exerted  by  certain  gases  when  gen- 
erated in  closed,  strong  glass  vessels  was  also 
employed  as  a  means  of  compression. 

The  low  temperatures  were  produced  by  means 
of  a  bath  of  Thilorier's  mixture  of  solid  carbonic 
acid  and  ether.  This  mixture  was  allowed  to 
evaporate,  at  the  ordinary  atmospheric  pressure, 
in  an  open  earthenware  dish  which  rested  in  a 
second  larger  vessel;  the  space  between  the  two 
being  filled  with  dry  flannel.  Faraday  modified 
the  method,  however,  and  obtained  a  much  lower 
temperature  by  evaporating  the  mixture  under 
reduced  pressure. 

The  influence  of  pressure  is  shown  by  the  fol- 
lowing table :  — 


Pressure  in  Inches  of  Mercury 

Temperature  of  Mixture 

28.4 

-    70° 

19.4 

-    80.3 

9.4 

-    85 

7-4 

-    88.3 

5-4 

-    90.6 

3-4 

-  95 

2.4 

-  98.3 

1.4 

—  106.6 

1.2 

-no  =  -  i66°F. 

The  temperatures  were  measured  by  means  of 
an  alcohol  thermometer,  and  Faraday  remarks  that 


EXPERIMENTS   OF  FARADAY  47 

the  actual  temperatures  were  probably  from  5  to 
6°  lower  than  those  recorded. 

The  gases  were  condensed  in  tubes,  the  forms 
of  which  are  shown  in  figures  6  and  7.  "These 
tubes  were  of  green  bottle  glass,  being  from  J  to  ^ 


FIG.  6. 

of  an  inch  in  external  diameter,  and  from  -fa  to  -fa 
of  an  inch  in  thickness.  They  were  chiefly  of  two 
kinds,  about  1 1  and  9  inches  in  length,  the  one, 
when  horizontal,  having  a  curve  downward  near 
the  end  to  dip  into  the  cold  bath,  and 
the  other,  being  in  form  like  an  inverted  <Q{) 

siphon,  could  have  the  bend  cooled  in 
the  same  manner  when  necessary.  In- 
to the  straight  part  of  the  horizontal 
tube,  and  the  longer  leg  of  the  siphon 
tube,  pressure-gauges  were  introduced 
when  required.  Caps,  stop-cocks,  and 
connecting  pieces  were  employed  to 
attach  the  glass  tubes  to  the  pumps, 
and  these,  being  of  brass,  were  of  the 
usual  character  of  those  employed  for 
operations  with  gases,  except  that  they  were  small 
and  carefully  made." 

These  tubes  were  tested  by  means  of  a  hydro- 


48  LIQUEFACTION   OF   GASES 

static  press.  One  of  them  sustained  a  pressure  of 
118  atmospheres  without  breaking,  while  another 
burst  at  a  pressure  of  67  atmospheres. 

The  pressures  were  measured  by  means  of  a 
small  glass  tube  which  contained  a  movable  cylin- 
der of  mercury,  one  end  of  the  tube  being  closed. 
A  pressure  of  10  or  20  atmospheres  would  reduce 
the  volume  of  air  in  the  gauge  to  ^  or  ^  of  its 
volume  at  the  ordinary  atmospheric  pressure. 
After  the  tube  had  once  been  calibrated,  it  was 
a  simple  matter  to  measure  the  various  pressures. 

The  solid  carbonic  acid  was  preserved  for  ex- 
perimental purposes  by  placing  it  in  a  glass  vessel, 
which  rested  in  the  middle  of  three  concentric  glass 
jars,  separated  from  each  other  by  dry  jackets  of 
woollen  cloth.  This  method  proved  to  be  very 
effectual.  The  results  obtained  are  as  follows  :  - 

Olefiant  Gas 

This  gas  was  condensed  to  a  clear,  colorless, 
transparent  liquid,  but  could  not  be  solidified  at 
the  lowest  temperature  obtainable  by  means  of  the 
carbonic  acid  mixture.  The  author  made  a  large 
series  of  observations  on  the  vapor  pressures  of 
this  liquid  at  different  temperatures.  He  also  sug- 
gested condensation  and  evaporation  as  a  method 
of  purifying  the  gas. 


EXPERIMENTS   OF   FARADAY  49 

Hydriodic  Acid 

This  gas  was  easily  condensed  by  means  of  the 
carbonic  acid  bath.  At  a  temperature  of  about 
—  51°  it  became  a  clear,  transparent,  colorless 
solid,  which  exhibits  fissures  or  cracks  similar  to 
those  in  ordinary  ice. 

Hydrobromic  Acid 

This'  gas  became  liquid  at  a  temperature  of 
about  —73°.  The  fluid  was  colorless  and  trans- 
parent. At  and  below  —  87°  it  is  a  solid,  transpar- 
ent, crystalline  body.  The  liquid  does  not  freeze 
until  reduced  much  lower  than  the  above-mentioned 
temperature,  but  being  frozen  by  the  carbonic  acid 
bath,  it  remains  a  solid  until  the  temperature,  in 
rising,  attains  to  —87°. 

Flnosilicon 

At  a  pressure  of  9  atmospheres  and  a  tempera- 
ture of  - 107°,  this  substance  condensed  to  a 
liquid.  In  this  condition  it  was  clear,  transparent, 
colorless,  and  very  fluid,  like  hot  ether.  It  could 
not  be  solidified  at  the  lowest  temperature  em- 
ployed in  these  experiments. 

Phosphine  and  Arsine 

Phosphine  was  liquefied,  but  could  not  be  solidi- 
fied. Faraday  remarks  that  in  this  experiment 


50  LIQUEFACTION   OF   GASES 

he  was  able  to  condense  only  a  portion  of  the  gas, 
and  suggests  the  presence  of  another  gas  which 
could  not  be  condensed  under  the  conditions  of 
the  experiment.  This  gas,  he  says,  is  probably 
another  phosphuretted  hydrogen,  or  hydrogen 
itself. 

In  regard  to  arsine,  he  says,  "  this  body,  lique- 
fied by  Dumas  and  Soubeiran,  did  not  solidify  at 
the  lowest  temperature  to  which  I  could  submit  it, 
i.e.  not  at  110°  below  zero." 

Fluoboron 

This  substance  was  prepared  from  fluorspar, 
fused  boracic  acid,  and  strong  sulphuric  acid,  in 
a  tube  generator,  and  conducted  into  a  condensing 
tube  under  the  generating  pressure.  The  ordi- 
nary carbonic  acid  bath  did  not  condense  it,  but 
the  application  of  one  cooled  under  the  air-pump 
produced  liquefaction.  Fluoboron  then  appeared 
as  a  very  limpid,  colorless,  clear  liquid,  showing 
no  signs  of  solidification.  At  the  lowest  tempera- 
ture it  appeared  as  mobile  as  hot  ether. 

Muriatic,  Sulphurous,  and  Carbonic  Acids 

All  attempts  to  solidify  muriatic  acid  were  un- 
successful. 

Sulphurous  acid,  at  —  76°,  became  a  crystalline, 


EXPERIMENTS   OF   FARADAY  51 

transparent,  colorless  solid,  which  sank  freely  into 
the  liquid. 

In  regard  to  carbonic  acid,  Faraday  says,  "  The 
solidification  of  carbonic  acid  by  Thilorier  is  one 
of  the  most  beautiful  experimental  results  of 
modern  times.  When  the  acid  is  melted  and  re- 
solidified by  a  bath  of  low  temperature,  it  appears 
as  a  clear,  transparent,  crystalline,  colorless  body, 
like  ice  ;  so  clear,  indeed,  that  at  times  it  was 
doubtful  to  the  eye  whether  anything  was  in  the 
tube." 

Euchlorine  and  Sulphuretted  Hydrogen 

Euchlorine  was  easily  condensed  to  a  crystalline 
solid,  the  color  and  appearance  of  which  were 
similar  to  those  of  potassium  bichromate ;  it  was 
moderately  hard,  brittle,  and  translucent.  The 
solid  melted  at  a  temperature  of  —60°.  In  at- 
tempting to  resolidify  the  substance,  a  peculiar 
phenomenon  was  observed.  The  author  remarks  : 
"  Some  hours  after,  wishing  to  solidify  the  same 
portion  of  euchloriae  which  was  then  in  a  liquid 
state,  I  placed  the  tube  in  a  bath  at  —80°,  but 
could  not  succeed  either  by  continuance  of  the 
tube  in  the  bath,  or  shaking  the  fluid  in  the  tube ; 
but  when  the  liquid  euchlorine  was  touched  by  a 
platinum  wire  it  instantly  became  solid,  and  exhib- 
ited all  the  properties  before  described.  There  are 


52  LIQUEFACTION   OF   GASES 

many  similar  instances  among  ordinary  substances, 
but  the  effect  in  this  case  makes  me  hesitate  in 
concluding  that  all  gases  which  as  yet  have  re- 
fused to  solidify  at  temperatures  as  low  as  —  110°, 
cannot  acquire  the  solid  state  at  such  a  tem- 
perature." 

Sulphuretted  hydrogen,  at  a  temperature  of 
—  85°,  solidified  to  a  white,  crystalline,  translucent 
substance,  which  was  made  up  of  a  confused  mass 
of  crystals. 

Ammonia  and  Cyanogen 

Ammonia  was  condensed  to  a  white,  translucent, 
crystalline  solid,  which  melted  at  a  temperature  of 
-85°. 

Cyanogen  was  also  obtained  as  a  transparent 
crystalline  solid,  the  specific  gravity  of  which  was 
nearly  the  same  as  that  of  the  liquid. 

Nitrous  Oxide 

This  gas  was  solidified,  at  a  temperature  of 
-i  00°,  to  a  beautiful,  clear,  crystalline,  colorless 
body.  The  pressure  of  the  vapor  rising  from  the 
solid  was  less  than  one  atmosphere.  Hence  "  it 
was  concluded  that  liquid  nitrous  oxide  could  not 
freeze  itself  by  evaporation  into  the  atmosphere, 
as  carbonic  acid  does;  and  this  was  found  to  be 


EXPERIMENTS   OF   FARADAY 


53 


true."  Natterer  observed  the  same  fact  a  year 
earlier.  Faraday  called  attention  to  the  fact  that 
very  low  temperatures  could  be  obtained  by  the 
evaporation  of  nitrous  oxide.  He  says :  "  It  is 
probable  that  this  substance  may  be  used  in  cer- 
tain cases,  instead  of  carbonic  acid,  to  produce 
degrees  of  cold  far  below  those  which  the  latter 
body  can  supply.  .  .  .  There  is  no  doubt  that  the 
substance  placed  in  vacuo  would  acquire  a  tem- 
perature lower  than  any  as  yet  known." 

Faraday  made  a  large  series  of  observations  on 
the  vapor  pressures  of  these  condensed  gases  at 
different  temperatures.  The  following  table  con- 
tains one  result  from  each  of  the  different  sub- 
stances :  — 


Substance 

Temperature 

Pressure 

0° 

43  4  atmospheres 

Hydriodic  acid       .... 

0° 

3-97        " 

Fluosilicon                       • 

0° 

7O  O                " 

Fluoboron 

0 

IO  O              " 

J  3 

Muriatic  acid 

0° 

26  2              " 

Sulphurous  acid     .... 

0° 

1.53            « 

Sulphuretted  hydrogen   .     . 

0° 

10.  0              " 

Carbonic  acid   

0° 

38.5 

Cyanogen     

0° 

2.37 

Ammonia     

0° 

4.44 

Arsine 

0° 

8  95         " 

Nitrous  oxide    

0° 

32.0          " 

54  LIQUEFACTION   OF   GASES 

The  following  substances  could  not  be  solidified 
at  a  temperature  of  —  110°:  chlorine,  ether,  alco- 
hol, carbon  disulphide,  caoutchoucine,  camphine, 
and  oil  of  turpentine. 

Faraday  also  attempted  to  liquefy  the  so-called 
permanent  gases  by  subjecting  them  to  low  tem- 
peratures and  high  pressures,  but  without  success. 
At  the  lowest  temperature  obtainable  by  means  of 
the  carbonic  acid  mixture,  these  gases  were  sub- 
jected to  the  pressures  expressed  in  the  following 
table:  — 


Atmospheres 

Hydrogen       ....                           . 

27 

Oxygen 

eg 

Nitrogen   ...                                     . 

30 
CQ 

Nitric  oxide 

j^ 
CQ 

Carbon  monoxide 

4.O 

Coal  gas 

•7,2 

In  no  case  were  there  any  signs  of  liquefaction. 
The  author  says :  "  Thus,  though  as  yet  I  have 
not  condensed  oxygen,  hydrogen,  or  nitrogen,  the 
original  objects  of  my  pursuit,  I  have  added  six 
substances,  usually  gaseous,  to  the  list  of  those 
that  could  previously  be  shown  in  the  liquid  state, 
and  have  reduced  seven  to  the  solid  form." 

Although  Faraday  was  unsuccessful  in  his  at- 


EXPERIMENTS   OF   FARADAY  55 

tempts  to  liquefy  the  so-called  permanent  gases, 
yet  he  predicted  that  if  the  temperature  could  be 
sufficiently  reduced,  these  gases  would  pass  into 
the  liquid  or  solid  state.  The  behavior  of  gases 
and  vapors  at  different  temperatures,  he  says, 
"  gives  great  encouragement  to  the  continuance 
of  those  efforts  which  are  directed  to  the  conden- 
sation of  oxygen,  hydrogen,  and  nitrogen,  by  the 
attainment  and  application  of  lower  temperatures 
than  those  yet  applied.  If  to  reduce  carbonic 
acid  from  the  pressure  of  two  atmospheres  to  that 
of  one,  we  require,  then,  to  abstract  only  about 
half  the  number  of  degrees  that  is  necessary  to 
produce  the  same  effect  with  sulphurous  acid,  it 
is  to  be  expected  that  a  far  less  abstraction  will 
suffice  to  produce  the  same  effect  with  nitrogen  or 
hydrogen,  so  that  further  diminution  of  tempera- 
ture, and  improved  apparatus  for  pressure,  may 
very  well  be  expected  to  give  us  these  bodies  in 
the  liquid  or  solid  state." 

After  such  an  elaborate  series  of  observations,  it 
is  not  surprising  to  find  that  Faraday  anticipated 
the  work  of  Andrews  on  critical  constants.  He 
makes  the  following  statement :  "  M.  Cagnaird  de 
la  Tour  has  shown  that  at  a  certain  temperature 
a  liquid,  under  sufficient  pressure,  becomes  clear, 
transparent  vapor,  or  gas,  having  the  same  bulk 
as  the  liquid.  At  this  temperature,  or  one  a  little 


56  LIQUEFACTION    OF   GASES 

higher,  it  is  not  likely  that  any  increase  of  pressure, 
except  perhaps  one  exceedingly  great,  would  con- 
vert the  gas  into  a  liquid.  Now  the  temperature 
of  110°  below  zero,  low  as  it  is,  is  probably  above 
this  point  of  temperature  for  hydrogen,  and  per- 
haps for  nitrogen  and  oxygen,  and  then  no  com- 
pression, without  the  conjoint  application  of  a 
degree  of  cold  below  that  we  have  as  yet  obtained, 
can  be  expected  to  take  from  them  their  gaseous 
state.  Further,  as  ether  assumes  this  state  before 
the  pressure  of  its  vapor  has  acquired  38  atmos- 
pheres, it  is  more  than  probable  that  gases  which 
can  resist  the  pressure  of  from  27  to  57  atmos- 
pheres at  a  temperature  of  —  110°  could  never 
appear  as  liquids,  or  be  made  to  lose  their  gaseous 
state  at  ordinary  temperatures.  They  may  proba- 
bly be  brought  into  the  state  of  very  condensed 
gases,  but  not  liquefied." 

EXPERIMENTS  OF  NATTERER 

In  1844  Natterer1  published  an  article  on  the 
liquefaction  and  solidification  of  carbonic  acid, 
nitrous  oxide,  etc.  Historically  considered,  this 
work  should  precede  the  experiments  of  Faraday, 
which  have  just  been  outlined.  The  observations 
of  Natterer,  however,  extend  over  a  period  of  a 

1  Jour.  Prakt.  Chem.,  31,  p.  375;   Pogg,  Ann.,  62,  p.  132,  1844. 


EXPERIMENTS   OF   NATTERER  57 


LIQUEFACTION   OF  GASES 


number  of  years, 
and  for  that  reason 
are  taken  up  at 
this  point. 

The  methods 
employed  in  the 
liquefaction  of 
gases  were  mate- 
rially advanced  by 
this  investigator. 
He  placed  in  the 
hands  of  the  ex- 
perimenters a 
method  for  obtain- 
ing extremely  high 
pressures.  He  also 
introduced  a  con- 
venient vessel  for 
preserving  lique- 
fied gases. 

A  sketch  of  the 
complete  appa- 
ratus l  employed 
by  Natterer  is 
shown  in  figure  8. 
The  details  can  be 

1  Jour.  Prakt.  Chem., 
35,  p.  169. 


EXPERIMENTS   OF  NATTERER  59 

seen  from  figures  9  and  10.  The  tube  A  (Fig.  9) 
is  provided  on  one  end  with  a  screw.  This  end 
of  the  tube  is  screwed  air-tight  into  an  opening 
in  the  cylinder  B  of  the  pump,  and  is  fastened 
in  that  position  by  means  of  the  ring  A'.  The 
other  end  of  the  tube  A  is  provided  with  notches, 
so  that  it  can  be  fastened  to  a  flexible  leather 
or  rubber  sack.  This  sack  is  connected  with  a 
receiver,  in  which  the  gas  to  be  compressed  is 
kept.  The  cylinder  B  of  the  pump  is  an  iron 
tube,  about  20  inches  in  length  and  0.6  inches  in 
diameter.  It  consists  of  two  tubes  screwed  into 
a  larger  short  section  B' .  In  the  interior  of  the 
cylinder  is  a  piston  C  (Fig.  10),  provided  with  a 
leather  cap,  and  fastened  to  the  piston  rod  D.  On 
turning  the  contrivance  G',  the  piston  is  moved  up 
and  down.  At  the  lowest  position  the  piston  is 
below  the  inlet  tube  A.  The  wrought-iron  vessel 
G  is  provided  at  the  bottom  with  a  valve  which 
opens  inward,  and  at  the  top  with  an  outlet  cock  g. 
The  vessel  G  has  a  capacity  of  about  20  litres.  A 
freezing  mixture  is  placed  in  the  chamber  H.  The 
receivers  were  always  tested,  before  use,  to  a  press- 
ure of  1 50  atmospheres.1 

1  The  apparatus  of  Natterer  has  been  improved  by  Bianchi  in 
Paris,  and  later  by  Ritchie  in  Boston. 


60  LIQUEFACTION   OF   GASES 

Condensation  of  Carbonic  Acid 

The  gas  to  be  liquefied  was  first  dried  by  pass- 
ing through  a  bottle  containing  calcium  chloride. 
The  pump  was  then  started,  and  the  cock  g 
opened.  When  all  the  air  had  been  removed  from 
the  pump  and  receiver,  the  cock  was  closed  and 
the  compression  begun.  The  cooling  was  accom- 
plished by  means  of  ice  water  in  the  vessel  H. 
The  operation  required  from  one  to  one  and  a  half 
hours.  In  this  way  Natterer  obtained  liquid  car- 
bonic acid  in  considerable  quantity.  The  liquid 
could  be  kept  in  the  receiver  for  several  months. 
He  also  obtained  large  quantities  of  solid  carbonic 
acid  and  studied  its  properties. 

Nitrous  Oxide 

Natterer  was  the  first  to  obtain  large  quantities 
of  liquid  nitrous  oxide.  He  found  the  boiling 
point  to  be  —  105°.  He  also  solidified  the  gas  and 
filtered  the  solid  out  of  the  liquid.  The  freezing 
point  was  found  to  be  —  1 15°. 

Experiments  on  Air,  Oxygen,  Hydrogen,  etc.1 

Natterer  subjected  carbon  monoxide  to  a  press^ 
ure  of  150  atmospheres,  but  observed  no  indi- 

1  Wien.  Ber.,  5,  p.  351;  6,  pp.  557  and  570;   12,  p.  199. 


EXPERIMENTS   OF   BERTHELOT  61 

cations  of  liquefaction.  This  induced  him  to 
construct  an  apparatus,  by  means  of  which  a 
pressure  of  1000  atmospheres  could  be  obtained. 
With  this  apparatus  he  hoped  to  condense  the  so- 
called  permanent  gases  to  the  liquid  state.  This 
hope,  however,  was  not  realized.  Only  negative 
results  were  obtained.  He  then  modified  the 
apparatus,  and  subjected  the  gases  to  pressures 
as  high  as  3600  atmospheres  (54,000  pounds  per 
square  inch),  and  concluded  that  with  pressure 
alone  these  gases  could  not  be  liquefied.  He  next 
endeavored  to  combine  the  high  pressure  with  low 
temperature,  but  without  success.  The  low  tem- 
perature was  obtained  by  means  of  solid  carbonic 
acid  and  ether. 

The  experiments  of  Natterer,  although  unsuc- 
cessful as  far  as  the  liquefaction  of  the  permanent 
gases  is  concerned,  show  that  these  gases  under 
high  pressures  deviate  considerably  from  Boyle's 
law.  Further  reference  to  these  variations  will 
be  made  at  the  end  of  the  chapter. 

EXPERIMENTS  OF  BERTHELOT 

In  1850  Berthelot1  constructed  an  apparatus, 
by  means  of  which  gases  could  be  liquefied  with- 
out danger.  The  pressure  was  obtained  by  the 

Compt.  rend.,  30,  p.  666. 


62  LIQUEFACTION   OF  GASES 

dilation  of  a  liquid.  The  apparatus  consisted 
simply  of  a  thick-walled  glass  tube  which  was 
closed  at  one  end.  The  tube  was  filled  with  pure 
dry  mercury  free  from  air,  and  then  drawn  out 
into  a  capillary  .at  the  open  end.  The  large  end 
of  the  tube  was  placed  in  a  water  bath,  and  the 
capillary  portion  in  a  current  of  the  gas  to  be 
compressed.  The  water  bath  was  then  heated, 
and  a  portion  of  the  mercury  expelled.  On  cool- 
ing, the  mercury  contracted,  and  the  portion  which 
had  been  expelled  was  replaced  by  the  gas.  The 
capillary  portion  of  the  tube  was  then  sealed,  and 
the  water  bath  again  heated. 

Berthelot  succeeded,  with  tubes  of  this  kind,  in 
condensing  chlorine,  ammonia,  and  carbonic  acid 
to  the  liquid  state.  He  observed  the  abnormal  ex- 
pansion of  liquid  carbonic  acid,  which  was  pointed 
out  by  Thilorier.  Berthelot  also  endeavored  to 
liquefy  nitric  oxide,  carbon  monoxide,  and  oxy- 
gen. The  results  in  these  cases,  however,  were 
negative.  The  pressure  obtained  in  the  experi- 
ment on  oxygen  was  about  780  atmospheres. 
The  temperature  of  the  gas  in  this  case  was 
lowered  by  means  of  solid  carbonic  acid.  Ber- 
thelot came  to  the  conclusion  that  pressure  would 
not  produce  liquefaction  under  all  conditions  of 
temperature. 


EXPERIMENTS    OF   DRION  63 

OBSERVATION  OF  DRION 

In  1859  Drion1  made  some  observations  similar 
to  those  made  by  Andrews  a  few  years  later.  The 
experiments,  however,  were  not  very  elaborate. 
Working  with  hydrochloric  ether,  nitrogen  tetrox- 
ide,  and  sulphurous  acid,  he  found  that  the  coef- 
ficient of  expansion  of  these  substances  in  the 
liquid  state  increases  very  rapidly  with  increasing 
temperature. 

He  also  observed  that,  when  the  liquids  were 
gradually  heated  in  closed  tubes  to  the  tempera- 
ture of  complete  vaporization,  the  surfaces  lost 
their  definition  and  reflecting  power,  and  became 
nebulous  in  appearance.  The  nebulous  zone  in- 
creased in  size  both  upward  and  downward,  and 
at  the  same  time  became  less  distinct  until  the 
tube  appeared  entirely  empty.  Similar  appear- 
ances were  produced  in  the  inverse  order  by 
gradually  cooling  the  tube. 

When  a  capillary  tube  was  partially  immersed  in 
the  liquid,  the  curvature  of  the  meniscus  and  the 
capillary  elevation  gradually  decreased  as  the 
temperature  rose,  and  finally,  just  before  complete 
vaporization,  the  surface  became  plane,  and  the 
level  of  the  liquid  within  the  tube  was  the  same  as 
that  of  the  liquid  without  the  tube. 

1  Ann.  de  Chim.  et  de  Phys.  [3],  pp.  5  and  221. 


64  LIQUEFACTION   OF   GASES 

Later,  Drion  and  Loir l  described  a  method  for 
liquefying  gases  in  considerable  quantity.  They 
lowered  the  temperature  by  the  method  of  Bussy ; 
i.e.  by  the  evaporation  of  volatile  liquids.  These 
experimenters,  however,  modified  the  method  by 
conducting  finely  divided  currents  of  dry  air 
through  the  liquid  during  evaporation.  In  this 
way  Drion  and  Loir  succeeded  in  liquefying  a 
number  of  gases,  and  studied  their  properties. 
The  low  temperatures  were  measured  by  means  of 
an  alcohol  thermometer. 

During  the  following  year  these  experimenters2 
succeeded  in  obtaining  a  perfectly  transparent 
mass  of  solid  carbonic  acid.  The  temperature  was 
lowered  by  the  evaporation  of  liquid  sulphurous 
acid  and  ammonia.  The  transparent  mass  of 
carbonic  acid,  they  state,  consisted  of  cubical 
crystals. 

OBSERVATIONS  OF  MENDELEEFF 

In  1861  Mendeleeff  called  attention  to  some 
important  relations  between  the  gaseous  and  liquid 
states  of  matter.  In  the  concluding  paragraph  to 
an  article  on  "  The  Expansion  of  Liquids  when 
Heated  above  their  Boiling  Points,"  3  he  makes  the 

1  Phil.  Mag.  [4],  20,  p.  202,  1860. 
*Itrid.  [4],  21,  p.  495,  1861. 
8  Lieb.  Ann.,  119,  p.  i,  1861. 


EXCEPTIONS   TO   BOYLE'S    LAW  65 

following  statement :  The  absolute  boiling  point  of 
a  liquid  is  that  temperature  at  which  the  cohesion 
and  the  heat  of  vaporization  become  equal  to  zero. 
At  this  temperature  the  liquid  changes  to  vapor, 
regardless  of  the  pressure  and  volume.  The 
absolute  boiling  point  of  alcohol  he  determined  to 
be  250°,  and  that  of  water  580°.  The  absolute 
boiling  point  suggested  by  Mendeleeff  corresponds 
to  the  critical  temperature  introduced  by  Andrews 
(see  next  chapter). 

EXCEPTIONS  TO  BOYLE'S  LAW 

Before  closing  the  present  chapter,  reference 
should  be  made  to  some  observations  on  the  rela- 
tion of  pressure  to  the  volume  of  a  gas.  These 
experiments  were  made  for  most  part  to  test  the 
validity  of  Boyle's  law.  Van  Marum,  in  1799(566 
p.  15),  called  attention  to  the  fact  that  ammonia  gas 
at  high  pressures  does  not  obey  this  law.  Other 
isolated  experiments  have  been  recorded,  but  for 
the  present  purpose  we  may  begin  with  the  obser- 
vations of  Despretz1  in  1827.  He  determined  the 
relative  compressibilities  of  a  number  of  gases. 
The  volumes  of  the  different  gases  at  the  begin- 
ning of  the  experiment  were  equal  to  each  other, 
but  as  the  pressure  was  increased,  this  equality  of 

1  Ann.  de  Chini.  et  de  Phys.  [2],  34,  p.  335. 
F 


66  LIQUEFACTION   OF  GASES 

volumes  was  destroyed.  Carbonic  acid  and  am- 
monia were  found  to  be  more  compressible  than 
air.  At  pressures  above  15  atmospheres,  he 
noticed  that  the  volume  of  air  was  slightly  less  than 
that  of  hydrogen.  Similar  observations  were  made 
by  Pouillet.  In  1830  Arago  and  Dulong1  experi- 
mented with  air  at  pressures  ranging  from  i  to  27 
atmospheres.  In  these  experiments  the  observed 
volume  was  usually  somewhat  less  than  that  calcu- 
lated from  Boyle's  law. 

In  1854  Natterer  studied  the  effect  of  exceed- 
ingly high  pressures  on  oxygen,  nitrogen,  air,  and 
hydrogen.  He  subjected  these  gases  to  pressures 
of  more  than  3000  atmospheres.  The  apparatus 
consisted  simply  of  a  compression-pump  and  a 
receiver,  which  was  provided  with  a  manometer. 
The  quantity  of  gas  which  the  receiver  contained 
at  the  ordinary  atmospheric  pressure  was  increased 
10,  20,  50,  and  100  fold,  and  so  on,  and  the  corre- 
sponding pressures  measured.  The  following  table  2 
contains  some  of  the  results.  The  numbers  in  the 
first  column  under  each  gas  represent  the  volumes 
which  were  forced  into  the  receiver,  while  those 
in  the  second  column  represent  the  corresponding 
pressures  in  atmospheres. 


1  Ann.  de  Chim.  et  de  Phys.  [2],  43,  p.  74. 
z  Wien.  Ber.,  12,  pp.  204-206,  1854. 


EXCEPTIONS  TO   BOYLE'S   LAW 


HYDROGEN 

OXYGEN 

NITROGEN 

Volume 

Pressure 

Volume    Pressure 

Volume 

Pressure 

8 

8 

7 

7 

5 

5 

18 

18 

17 

17 

15 

15 

28 

28 

27 

27 

25 

25 

38 

38 

37 

37 

35 

35 

48 

48 

47 

47 

45 

45 

58 

58 

57 

57 

55 

55 

68 

68 

67 

67 

65 

65 

78 

78 

77 

77 

75 

75 

88 

89 

87 

87 

85 

85 

98 

100 

97 

97 

95 

96 

198 

222 

117 

117 

195 

206 

298 

352 

147 

147 

295 

336 

398 

505 

177 

177 

395 

542 

598 

930 

187 

1  88 

495 

882 

798 

1584 

207 

210 

595 

1546 

928 

2154 

507 

670 

705 

2790 

1008 

2790 

657 

1354 

A  glance  at  this  table  will  show  that  the  meas- 
urements were  only  approximations.  There  can 
be  no  doubt  from  the  results,  however,  that  these 
gases  under  high  pressures  deviate  from  Boyle's 
law.  The  relative  deviations  increase  with  increas- 
ing pressure. 

Regnault 1  investigated  this  subject  more  thor- 
oughly. He  introduced  the  gas  into  an  accurately 


1  Mem.  de  I'Acad.,  21,  p   329. 


68 


LIQUEFACTION   OF   GASES 


calibrated  glass  tube,  which  was  kept  at  a  uniform 
temperature.  The  gas  was  then  compressed  to  a 
certain  fraction  of  the  initial  volume  by  means  of 
mercury,  and  the  pressure  again  measured.  If  the 
initial  pressure  and  volume  be  represented  by  /0 
and  Vty  and  the  final  pressure  and  volume  by  / 
and  v,  the  following  table l  will  show  that  the  prod- 
uct of  the  pressure  and  volume  does  not  remain 
constant. 

In  every  case,  except  hydrogen,  the  compressi- 


AIR 

NITROGEN 

A 

Pv 

A 

^ 

mm. 

mm. 

738.72 

1.001414 

75346 

1.000988 

2112.53 

1.002765 

4953-92 

1.002952 

4140.82 

1.003253 

8628.54 

1  .004768 

9336.41 

1.006366 

10981.42 

1  .006456 

CARBON  DIOXIDE 

HYDROGEN 

A 

£ 

A 

Pv 

mm. 

mm. 

764.03 

1.007597 

.  .  . 

.  .  . 

3186.13 

1.028698 

22II.I8 

0998584 

4879  77 

I  045625 

5845.18 

0.996121 

9619.97 

1.155865 

9176.50 

0.992923 

1  Preston,  Theory  of  Heat,  p  402. 


EXCEPTIONS   TO   BOYLE'S   LAW  69 

bility  was  found  to  be  greater  than  that  calculated 
from  Boyle's  law.  The  compressibility  of  hydro- 
gen was  found  to  be  less  than  the  calculated  value. 
Owing  to  this  peculiar  behavior,  Regnault  distin- 
guished hydrogen  as  a  gaz  plus  que  parfait. 

During  the  last  thirty  years  this  subject  has 
been  very  thoroughly  investigated  by  Cailletet, 
Amagat,  and  others.  The  results  of  these  obser- 
vations will  be  considered  in  the  next  chapter. 


CHAPTER    III 

SECTION    I 
Conception  of  Critical  Constants 

WHILE  the  investigations  on  Boyle's  law  were 
being  carried,  out,  Andrews  was  considering  the 
problem  of  the  liquefaction  of  gases.  With  his 
observations  a  new  era  begins.  Maxwell1  says, 
"The  experiments  of  Andrews  on  carbonic  acid 
furnish  the  most  complete  view  hitherto  given  of 
the  relation  between  the  gaseous  and  liquid  states 
of  matter,  and  of  the  mode  in  which  the  properties 
of  a  gas  may  be  continuously  and  imperceptibly 
changed  into  those  of  a  liquid."  The  question  as 
to  the  relative  value  of  temperature  and  pressure  in 
the  liquefaction  of  gases  had  long  been  discussed. 
The  interesting  observations  of  Caignard  de  la 
Tour  (p.  18),  of  Drion  (p.  63),  and  of  Mendeleeff 
(p.  64),  all  point  toward  the  conclusion  that  for 
every  gas  there  is  a  definite  temperature  above 
which  it  cannot  be  liquefied.  These  results,  how- 
ever, remained  unheeded  until  Andrews  published 

1  Theory  of  Heat,  p.  124. 
70 


CONCEPTION   OF   CRITICAL   CONSTANTS      71 

his  exhaustive  researches  in  this  field.  From  his 
observations  it  is  evident  that  for  every  gas  there 
is  a  definite  temperature  above  which  it  cannot 
be  condensed  to  the  liquid  state.  This  point 
Andrews  called  the  Critical  Temperature.  The 
Caignard  de  la  Tour  point,  to  which  Faraday 
frequently  referred,  and  the  absolute  boiling  point 
suggested  by  Mendeleeff,  correspond  to  this  same 
temperature. 

Previous  to  the  work  on  critical  constants, 
Andrews1  studied  the  effect  of  high  pressures 
and  low  temperatures  on  the  volumes  of  various 
gases.  He  experimented  at  temperatures  varying 
from  —75°  to  --110°.  Ordinary  air  was  com- 
pressed to  gi^  of  its  original  volume ;  in  which 
state  the  density  was  but  little  inferior  to  that  of 
water.  Oxygen  was  reduced  to  ^^,  and  hydrogen 
to  -g-Jfl-  of  the  original  volumes.  Experiments  were 
also  made  on  carbon  monoxide,  nitrogen,  and  nitric 
oxide.  None  of  the  gases  showed  any  indications 
of  liquefaction. 

The  results  obtained  in  the  preceding  experi- 
ments led  Andrews  to  make  a  careful  study  of 
the  conditions  under  which  carbonic  acid  can  be 
liquefied.  The  first  account  of  this  work  was 
communicated  by  the  author  to  Dr.  Miller,  who 

1  Chem.  News,  4,  p.  158,  1861. 


72  LIQUEFACTION   OF   GASES 

published  a  short  notice  of  the  results  in  I863.1 
The  note  reads  as  follows :  — 

"  On  partially  liquefying  carbonic  acid  by  press- 
ure alone,  and  gradually  raising  at  the  same  time 
the  temperature  to  88°  F.,  the  surface  of  demarka- 
tion  between  the  liquid  and  gas  became  fainter, 
lost  its  curvature,  and  finally  disappeared.  The 
space  was  then  occupied  by  a  homogeneous  fluid, 
which  exhibited,  when  the  pressure  was  suddenly 
diminished  or  the  temperature  slightly  lowered,  a 
peculiar  appearance  of  moving  or  flickering  striae 
throughout  the  entire  mass.  At  temperatures 
above  88°  no  apparent  liquefaction  of  carbonic 
acid,  or  separation  into  two  distinct  forms  of  mat- 
ter, could  be  effected,  even  when  a  pressure  of  300 
or  400  atmospheres  was  applied.  Nitrous  oxide 
gave  analogous  results." 

A  complete  account  of  the  first  series  of  obser- 
vations was  published  by  the  author  in  i869.2 
The  apparatus  employed  is  shown  in  figures  u, 
12,  and  13.  The  gas  to  be  liquefied  was  com- 
pressed in  glass  tubes  of  the  form  represented 
in  figure  u.  The  upper  portion,  from  a  to  b,  is 
a  capillary  tube.  From  b  to  c  the  diameter  is 
about  2.5  mm.,  and  from  c  to  f  about  1.25  mm. 
Before  use  the  tubes  were  carefully  calibrated  by 

1  Miller,  Chemical  Physics,  3d.  ed.,  p.  328. 

2  Bakerian  Lecture,  Trans.  Roy.  Soc.,  1869,  Part  2,  p.  575. 


CONCEPTION    OF   CRITICAL    CONSTANTS       73 


means  of  mercury.  The  pure,  dry,  carbonic  acid 
was  conducted  through  the  tube  for  several  hours, 
to  remove  the  air.  The  capillary  end  was  then 
hermetically  sealed,  and 
the  other  end  tempora- 
rily closed  until  the  tube 
was  placed  in  an  upright 
position  with  this  end 
below  the  surface  of 
mercury,  as  shown  in 
the  third  tube  (Fig.  11). 
Heat  was  then  applied 
to  the  tube  until  a  small 
quantity  of  the  gas  was 
expelled  through  the 
mercury.  On  cooling,  a 
short  column  of  mer- 
cury rose  in  the  tube. 
The  open  end,  while 
under  the  surface  of  the 
mercury,  was  then  con- 
nected with  the  receiver 
of  an  air-pump,  and  the  tube  partially  exhausted. 
In  this  way  the  mercury  could  be  made  to  rise  any 
desired  height.  The  tube  being  previously  cali- 
brated, it  was  a  simple  matter  then  to  accurately 
calculate  the  volume  of  the  gas  at  o°  and  760  mm 
pressure. 


'c 
e|n 


FIG.  ii. 


74 


LIQUEFACTION    OF   GASES 


The  tube  containing  the  gas,  with  a  small  quan- 
tity of  mercury,  was  placed  in  a  strong,  cold-drawn 
copper  tube,  provided  at  each  end  with  a  massive 
brass  flange.  A  longitudinal  section  of  this  ar- 
rangement is  shown  in  figure  12.  Two  brass  end- 


! 


FIG.  12. 

pieces  were  firmly  bolted  to  the  flanges,  and  the 
connection  made  air-tight  by  means  of  leather 
washers.  The  lower  end  of  the  tube  was  pro- 
vided with  a  steel  screw  180  mm.  in  length  and 
4  mm.  in  diameter.  By  means  of  this  screw  a 


CONCEPTION    OF   CRITICAL   CONSTANTS       75 

pressure  of  400  atmospheres  could  be  obtained. 
The  portion  of  the  copper  tube  not  occupied  by 
the  glass  tube  was  filled  with  water.  When  the 
screw  was  inserted,  the  pressure  gradually  in- 
creased ;  the  mercury  rose  in  the  glass  tube  and 
forced  the  gas  up  into  the  capillary  portion  which 
had  been  calibrated.  The  complete  apparatus  is 
represented  in  figure  13.  One  of  the  tubes  contains 
the  carbonic  acid,  while  the  other  contains  air  and 
serves  as  a  comparison  tube.  A  communication 
is  established  between  the  two  tubes  through  a  and 
b,  below  the  mercury,  so  that  the  pressures  will  be 
equal.  The  pressures  at  different  intervals  were 
calculated  from  the  relative  volumes  of  the  com- 
pressed air. 

At  a  temperature  of  13°.!,  the  carbonic  acid 
began  to  liquefy  under  a  pressure  of  48.89  atmos- 
pheres. This  point  could  not  be  observed  directly, 
inasmuch  as  the  first  visible  traces  of  liquid  repre- 
sent a  column  two  or  three  millimetres  in  length. 
It  was  determined  indirectly,  however,  by  observ- 
ing the  volume  of  the  gas  at  a  few  tenths  of  a 
degree  above  the  point  of  liquefaction,  and  then 
calculating  the  contraction  of  the  gas  in  cooling  to 
the  point  where  liquefaction  begins.  The  results 
obtained  at  the  temperatures  13°.!  and  21°.  5  are 
given  in  the  following  table,  in  which  S  represents 
the  ratios  of  the  volumes  of  air  before  and  after 


76 


LIQUEFACTION   OF   GASES 


compression,  e  represents  the  corresponding  ratios 
for  carbonic  acid,  t  is  the  temperature  of  the  air, 
and  /'  the  temperature  of  the  carbonic  acid :  — 


CARBONIC  ACID  AT  13°.! 

CARBONIC  ACID  AT  21°.  5 

5 

/ 

e 

/' 

& 

/ 

e 

t' 

i 
47-5° 

io°.75 

I 
76.16 

I3°.i8 

i 
46.70 

8°.63 

I 
67.26 

21°.  46 

4^89" 

10  .86 

i 
80.90 

13  .09 

60.05 

8  .70 

I 
114.7 

21    .46 

i 
49.00 

10  .86 

i 
105.9 

13  .09 

i 
60.29 

8  .70 

i 
I74~8 

21    .46 

49-28 

10  .86 

268.8 

13  .09 

60.55 

8  .70 

240.5 

21    .46 

i 
50-15 

10  .86 

i 
462.9 

13  .09 

i 
61  oo 

8  .70 

i 
367-7 

21    .46 

i 
76.61 

10  .86 

I 
500.7 

13  .09 

i 

62  21 

8  .70 

I 
440.0 

21   .46 

i 
90-43 

10  .86 

I 
5IO-7 

13  .09 

I 
62.50 

8  .70 

I 
443-3 

21   .46 

In  both  series  of  results  there  is  an  abrupt 
change  of  volume  at  the  point  where  liquefaction 
begins.  The  small  increase  in  pressure,  which 
was  necessary  to  continue  the  liquefaction,  was 
attributed  by  Andrews  to  a  small  quantity  of  air 
in  the  tube  containing  the  carbonic  acid.  After 
the  condensation  to  liquid  was  complete,  the  press- 
ure increased  rapidly.  The  high  coefficient  of 
expansion  of  liquid  carbonic  acid,  which  had  been 
observed  by  Thilorier,  was  confirmed  by  Andrews. 

The  following  table  gives  the  results  obtained 
at  the  temperatures  31°.  i  and  32°. 5  :  — 


CONCEPTION   OF   CRITICAL   CONSTANTS      77 


CARBONIC  ACID  AT  31°.! 

CARBONIC  ACID  AT  32°.  5 

I 

t 

€ 

'' 

S 

t 

e 

t' 

i 
54-79 

110.59 

I 
80.55 

3I--I7 

i 

12°.  10 

i 
859° 

32'.5o 

i 

II    .55 

I 
90.04 

3i  -19 

i 
71-52 

12  .15 

i 
I4°-3 

32  -34 

62.67 

II    .44 

I 
103.1 

3i  -19 

73.60 

12  .30 

i 
156.0 

32  -45 

i 
67.60 

II    .63 

124.4 

31  .15 

i 
7402 

12  .30 

i 
159-9 

32  .46 

i 
73.26 

II    .45 

I 
169.0 

31  .09 

i 
76.25 

12  .40 

19  .7 

32-38 

i 
73^83 

13  .00 

I 
174-4 

31  .08 

i 
78^52 

12  .50 

^-g 

32  -48 

i 
75-40 

II    .62 

I 

31  .06 

i 
79-77 

12  -35 

351-3 

32  -54 

i 
79.92 

II    .16 

I 

31  .10 

i 
84.90 

12  -35 

i 
3878 

32  -75 

i 
85-*9 

II    .45 

I 

4°5  5 

31  -°5 

In  these  experiments  there  was  no  evidence 
that  liquefaction  had  taken  place.  There  was  a 
sudden  decrease  in  volume  at  a  definite  pressure 
in  each  series,  just  as  in  the  preceding  observa- 
tions, but  the  fluid  in  this  case  did  not  separate 
into  two  distinct  layers. 

Observations  were  also  made  at  temperatures  of 
3 5°. 5  and  48°. i.  In  each  case  the  abruptness  of 
the  change  in  volume  becomes  less  marked  as  the 
temperature  increases.  The  results  may  be  best 
compared  by  reference  to  the  curves  (Fig.  14). 
The  ordinates  represent  the  pressures  in  atmos- 


LIQUEFACTION   OF   GASES 


pheres,  while   the   abscissas  represent  the  corre- 
ponding  volumes. 

The  curve  for  13°.!  shows  that  at  low  pressures 


-105 
'100 
95 
•90 

as 
ao 
73 

-70 
-65 
-60 
-55 
-SO 


FIG.  14. 

the  carbonic  acid  approximately  obeys  the  laws  of 
gaseous  expansion.  At  a  pressure  of  about  50 
atmospheres,  the  curve  becomes  almost  parallel 
to  the  axis  of  abscissas ;  i.  c.  the  volume  decreases 
rapidly  while  the  pressure  remains  practically  con- 


CONCEPTION   OF   CRITICAL  CONSTANTS      79 

stant.  This  represents  the  change  from  the  gas- 
eous to  the  liquid  state.  When  this  change  is 
complete,  the  pressure  increases  rapidly,  and  the 
curve  becomes  almost  parallel  to  the  axis  of  ordi- 
nates.  The  curve  for  21°. 5  is  very  similar  to  that 
for  1 3°.  i.  The  abruptness  of  the  change,  how- 
ever, is  not  quite  so  pronounced.  The  curves  for 
31°.  i  and  32°. 5  also  show  abrupt  changes,  after 
which  the  contraction  in  volume  corresponds 
approximately  to  that  of  liquid  carbonic  acid. 
However,  liquefaction  does  not  take  place  at  these 
temperatures.  At  48°.  i  the  curve  shows  no  abrupt 
changes.  Yet  at  high  pressures  the  gas  deviates 
considerably  from  Boyle's  law,  as  can  be  seen  by 
comparison  with  the  air  curves  in  the  same  figure. 
From  these  results  it  became  evident  to  An- 
drews that  carbonic  acid  can  be  liquefied  at  or 
below  the  temperature  of  21°.  5,  but  cannot  be 
liquefied  at  or  above  the  temperature  of  31°.!.  He 
then  made  a  series  of  careful  experiments  to 
determine  accurately  the  highest  temperature  at 
which  carbonic  acid  can  be  liquefied.  This  was 
found  to  be  30°. 92  C,  or  87°. 7  F.  Below  this  tem- 
perature two  distinct  layers  of  the  fluid,  separated 
by  a  well-defined  meniscus,  could  be  observed, 
while  at  higher  temperatures  no  such  separation 
could  be  produced.  This  point  is  the  critical 
temperature  of  carbonic  acid.  The  pressure  re- 


8o  LIQUEFACTION   OF   GASES 

quired  to  liquefy  carbonic  acid  at  this  temperature 
is  the  critical  pressure. 

The  change  of  state  at  the  critical  temperature 
is  gradual  and  imperceptible.  The  author  says, 
"  I  have  frequently  exposed  carbonic  acid  to  much 
higher  pressures,  and  have  made  it  pass,  without 
break  or  interruption,  from  what  is  regarded  by 
every  one  as  the  gaseous  state,  to  what  is,  in  like 
manner,  universally  regarded  as  the  liquid  state. 
Take,  for  example,  a  given  volume  of  carbonic 
acid  gas  at  50°,  or  at  a  higher  temperature,  and 
expose  it  to  increasing  pressure  until  150  atmos- 
pheres have  been  reached.  When  the  full  press- 
ure has  been  applied,  let  the  temperature  be 
allowed  to  fall  till  the  carbonic  acid  has  reached 
the  ordinary  temperature  of  the  atmosphere.  Dur- 
ing the  whole  of  this  operation  no  breach  of  con- 
tinuity has  occurred.  It  begins  with  a  gas,  and 
by  a  series  of  gradual  changes,  presenting  no- 
where any  abrupt  alteration  of  volume  or  sudden 
evolution  of  heat,  it  ends  with  a  liquid.  The 
closest  observation  fails  to  discover  anywhere  indi- 
cations of  a  change  of  condition  in  the  carbonic 
acid,  or  evidence  at  any  period  of  the  process  of 
part  of  it  being  in  one  physical  state,  and  part 
in  another.  That  the  gas  has  actually  changed 
into  a  liquid  would,  indeed,  never  have  been  sus- 
pected, had  it  not  shown  itself  to  be  so  changed 


CONCEPTION    OF   CRITICAL   CONSTANTS      81 

by  entering  into  ebullition  on  the  removal  of  the 
pressure." 

Andrews  extended  his  observations  to  ammo- 
nia, ether,  carbon  disulphide,  nitrous  oxide,  and 
hydrochloric  acid.  These  substances  exhibited 
properties  similar  to  those  of  carbonic  acid.  Their 
critical  temperatures  were  measured,  and  found,  in 
some  cases,  to  be  above  100°. 

Andrews  also  suggested  a  distinction  between 
gases  and  vapors  which  has  met  with  general 
approval.  This  distinction  is  based  upon  the 
critical  temperature.  Many  of  the  properties  of 
vapors,  he  says,  depend  on  the  gas  and  liquid 
being  present  together.  This  can  happen  only  at 
temperatures  below  the  critical  point.  A  vapor, 
therefore,  may  be  defined  as  a  gas  below  the 
critical  temperature.  A  vapor  can  be  condensed 
to  a  liquid  by  pressure  alone,  while  a  gas  cannot. 
Carbonic  acid,  then,  is  a  vapor  below  31°,  and 
a  gas  at  higher  temperatures.  Below  200°  ether 
is  a  vapor ;  above  that  temperature  it  is  a  gas.1 

Determination  of  Critical  Constants 

After  the  introduction  of  critical  constants  their 
measurement  became  a  matter  of  considerable  im- 

1  In  1876,  Andrews  extended  his  observations  to  much  higher 
temperatures,  but  with  similar  results.      Trans.  Roy.  Soc.,  1876, 
Part  2,  p.  421. 
G 


82  LIQUEFACTION    OF   GASES 

portance.  Most  of  the  experimenters  on  the  lique- 
faction of  gases  have  determined  critical  constants 
by  various  methods,  and  have  introduced  various 
definitions  for  the  critical  state.  The  simplest 
method  for  determining  the  critical  temperature 
and  critical  pressure  is  that  employed  by  Andrews. 
The  substance  is  placed  in  a  thick-walled  glass 
tube,  which  is  sealed  at  one  end.  The  highest 
temperature  at  which  the  liquid  meniscus  can  be 
formed  by  pressure  is  taken  as  the  critical  tempera- 
ture, and  the  corresponding  pressure  as  the  critical 
pressure. 

An  ingenious  method  has  been  introduced  by 
Cailletet  and  Colardeau1  for  the  determination  of 
the  critical  constants  of  substances,  such  as  water, 
which  attack  glass  at  high  temperature.  The 
operation  is  carried  out  in  a  steel  tube.  Numer- 
ous methods  have  also  been  introduced  by  other 
experimenters.2 

Critical  Constants  of  Gaseous  Mixtures 

Andrews  called  attention  to  the  fact  that  the 
presence  of  the  so-called  permanent  gases  lowered 
the  critical  temperature  of  such  gases  as  carbonic 
acid.  He  was  unable  to  liquefy  a  mixture  of  three 

1  Ann.  de  Chim.  et  de  Phys.  [6],  25,  p.  519. 

2  See  Heilborn  for  compilation  of  literature  on  critical  constants. 
Zeit.  phys.  Chem  n  7,  p.  601. 


CONCEPTION   OF   CRITICAL  CONSTANTS      83 

parts  of  carbonic  acid  with  four  parts  of  nitrogen 
at  temperatures  above  —  20°.  The  critical  tem- 
perature of  carbonic  acid  containing  one-tenth  of 
its  volume  of  air  or  nitrogen  was  found  to  be  con- 
siderably lower  than  that  of  the  pure  gas. 

Dewar l  made  a  large  series  of  observations  on 
the  liquefaction  of  mixtures  of  carbonic  acid  with 
various  substances.  He  thought  that  the  carbonic 
acid  probably  united  with  the  substance  to  form 
a  definite  compound  which  decomposed  when  the 
pressure  was  released. 

Pawlewski 2  worked  on  organic  compounds,  and 
concluded  that,  for  the  same  class  of  compounds, 
the  critical  point  of  the  mixture  lay  between 
those  of  the  two  constituents ;  and  he  thought 
that  the  interval  was  divided  proportionally  to  the 
quantities  of  the  compounds  present.  Ansdell,3 
on  the  other  hand,  maintained  that  this  law  does 
not  hold  true. 

During  recent  years  a  large  amount  of  work  has 
been  done  in  this  field.  The  references  to  these 
investigations,  however,  will  be  sufficient  for  the 
present  purpose.  See  especially  Dr.  Kuenen, 
Zeit.  phys.  CJiem.,  n,  p.  33;  and  Proc.  Phys.  Soc., 
Lond.,  13,  p.  523,  1895,  and  15,  p.  235,  1897; 

1  Proc.  Roy.  Soc.,  1880. 

2  Ber.  d.  d.  chem.  Ges.,  1882,  p.  460. 
8  Proc.  Roy.  Soc.,  34,  p.  113,  1882. 


84  LIQUEFACTION   OF   GASES 

Duhem,  Jour.  Phys.  Chem.,  I,  p.  273,  1897.  The- 
oretical, Van  der  Waals,  Zeit.  phys.  Ckern.,  5, 
P-  133- 

SECTION   II 

Continuity  of  the  Gaseous  and  Liquid  States  of 
Matter 

Since  the  introduction  of  critical  constants  by 
Andrews  much  discussion  has  arisen  concerning 
the  condition  of  matter  at  or  near  the  critical 
point.  Andrews  was  the  first  to  call  attention  to 
this  problem.  "  What  is  the  condition  of  carbonic 
acid,"  he  asks,  "  when  it  passes  at  temperatures 
above  31°,  from  the  gaseous  state  down  to  the 
volume  of  the  liquid,  without  giving  evidence  at 
any  part  of  the  process  of  liquefaction  having 
occurred  ?  Does  it  continue  in  the  gaseous  state, 
or  does  it  liquefy,  or  have  we  to  deal  with  a  new 
condition  of  matter  ?  If  the  experiment  were  made 
at  1 00°,  or  at  a  higher  temperature,  the  probable 
answer  would  be  that  the  gas  preserves  its  gaseous 
condition  during  the  compression.  On  the  other 
hand,  when  the  experiment  is  made  at  tempera- 
tures a  little  above  31°,  the  great  fall  which  occurs 
at  one  period  of  the  process  would  lead  to  the  con- 
jecture that  liquefaction  had  actually  taken  place, 
although  optical  tests  carefully  applied  failed  at 


CONTINUITY   OF   STATE  85 

any  time  to  discover  the  presence  of  liquid  in  con- 
tact with  a  gas.  .  .  .  Under  many  of  the  condi- 
tions which  I  have  described  it  would  be  vain  to 
attempt  to  assign  carbonic  acid  to  the  liquid  rather 
than  the  gaseous  state.  Carbonic  acid,  at  the  tem- 
perature of  3 5°. 5,  and  under  a  pressure  of  108 
atmospheres,  is  reduced  to  -^^  of  the  volume 
occupied  under  a  pressure  of  one  atmosphere ;  but 
if  any  one  ask  whether  it  is  now  in  the  gaseous  or 
liquid  state,  the  question  does  not,  I  believe,  admit 
of  a  positive  reply.  The  substance  in  this  condi- 
tion stands  nearly  midway  between  the  gas  and  the 
liquid." 

Numerous  observations  have  been  made  by  later 
experimenters  to  show  that  the  liquid  state  per- 
sists beyond  the  critical  point,  while  other  investi- 
gators have  endeavored  to  show  that  this  point  is 
the  limit  of  the  liquid  state. 

Avenarius1  made  a  series  of  observations  on 
"The  Causes  which  Determine  the  Critical  Point," 
and  concluded  that  the  volume  of  the  saturated 
vapor  at  the  critical  point  is  not  equal  to  that  of 
the  liquid  at  the  same  temperature.  He  experi- 
mented with  ether. 

Ansdell,2  on  the  other  hand,  experimenting  with 

J  Mem.  Acad.  Sci.,  St.  Petersburg,  1876-1877;  Ref.,  Ansdell, 
Proc,  Roy.  Soc.,  30,  p.  120. 

2  Proc.  Roy.  Soc.,  30,  p.  117,  1880. 


86 


LIQUEFACTION   OF   GASES 


hydrochloric  acid,  says,  "  The  volumes  of  the  satu. 
rated  vapor  and  liquid  gradually  approach  each 
other  as  the  temperature  nears  the  critical  point, 
and  would  undoubtedly  become  identical  if  the 
experiments  could  be  carried  on  up  to  the  critical 


-   750. 


-  120. 


10 


20  50 

FIG.  15. 


4-Q 


50 


point."  The  results  of  his  experiments  are  shown 
by  the  curves  in  figure  15.  The  volumes  are  rep- 
resented by  ordinates,  and  the  temperatures  by 
abscissas.  The  curve  a  represents  vapor  volumes, 


CONTINUITY   OF   STATE  87 

and  the  curve  b  liquid  volumes.  At  a  temperature 
slightly  above  50°,  the  curves  show  considerable 
change  in  direction.  Both  approach  the  critical 
point  x>  but  the  experiments  could  not  be  success- 
fully carried  to  this  temperature.1 

Ramsay2  says,  "The  critical  point  is  that  point 
at  which  the  liquid,  owing  to  expansion,  and  the 
gas,  owing  to  compression,  acquire  the  same  spe- 
cific gravity,  and  consequently  mix  with  each 
other." 

During  this  same  year,  Clark3  made  a  series 
of  experiments  with  sulphurous  acid  in  the  two 
branches  of  a  U-tube.  He  found  that  when  the 
temperature  was  near  the  critical  point,  the  disap- 
pearance of  the  meniscus  in  one  branch  did  not 
affect  the  level  of  the  liquid  in  the  other.  From 
this  he  concluded  that  the  density  of  the  vapor  at 
the  critical  point  is  equal  to  that  of  the  liquid. 

This  theory  seems  to  have  been  generally  ac- 
cepted. Thiesen4  says,  "A  substance  is  to  be 
considered  a  liquid,  or  gas,  according  as  the  den- 
sity is  greater  or  less  than  the  critical  density." 

1  Amagat  has  investigated  this  subject  more  thoroughly,  and 
says  the  density  of  the  vapor  rapidly  approaches  that  of  the  liquid 
at  the  critical  temperature.     Compt.  rend.,  114,  p.  1093.     See  also 
Cailletet  and  Mathias,  Jour,  de  Phys.  [2],  5,  p.  549,  1886. 

2  Proc.  Roy.  Soc.,  30,  p.  323,  1880. 

3  Proc.  Phys.  Sec.,  Lond.,  4,  p.  41,  1880. 

4  Zeit.  compr.  undfltiss.  Case,  I,  p.  87,  1897. 


88  LIQUEFACTION   OF   GASES 

Quite  recently,  however,  von  P.  de  Heen-Liittich 
has  published  an  article  entitled,  "  Uber  die  ange- 
blichen  Anomalieen  in  der  Nahe  des  kritischen 
Punktes,"  1  in  which  he  states  that  there  are  two 
critical  densities,  —  the  critical  density  of  the  liquid 
and  the  critical  density  of  the  vapor.  The  latter, 
he  says,  is  equal  to  one-half  of  the  former.  A 
large  number  of  observations  were  made,  and  the 
results  obtained  seem  to  contradict  some  of  the 
work  of  previous  experimenters.2 

The  condition  of  a  substance  at  or  near  the 
critical  point,  however,  has  been  more  thoroughly 
investigated  from  a  different  standpoint.  Hannay 
and  Hogarth3  examined  the  solvent  properties  of 
some  fluids  for  non-volatile  solids  during  the  pas- 
sage of  the  solvent  through  the  critical  point. 
A  precipitation  of  the  solid,  on  passing  through 
this  point,  they  thought,  would  be  conclusive  evi- 
dence of  a  change  from  liquid  to  gas.  If,  on  the 
other  hand,  the  solid  remained  in  solution,  it  would 
be  an  evidence  of  the  perfect  continuity  of  the 
gaseous  and  liquid  states. 

In  the  first  experiment  potassium  iodide  was 
dissolved  in  alcohol,  and  the  solution  heated  in  a 
closed  glass  tube.  There  was  no  indication  of  the 

1  Zeit.  compr.  undfliiss.  Case,  2,  pp.  97,  113,  and  134,  1898. 

2  See  also  M.  Gouy,  Compt.  rend.  115,  p.  720,  1892. 
8  Proc.  Roy.  Soc.,  30,  p.  178,  1880. 


CONTINUITY   OF   STATE  89 

separation  of  a  solid,  even  at  a  temperature  of 
350°,  which  is  nearly  100°  above  the  critical  point 
of  alcohol. 

The  next  experiment  consisted  in  dissolving  the 
crystals  of  potassium  iodide  in  alcohol  vapors. 
The  temperature  of  the  alcohol  was  never  lower 
than  65°  above  the  critical  point.  When  the  press- 
ure was  strongly  increased,  the  potassium  iodide 
dissolved.  By  releasing  the  pressure  rapidly,  fine 
crystals  of  the  salt  separated  out  as  a  film  on  the 
glass,  and  in  some  cases  as  'a  cloud  of  fine  particles, 
which  floated  about  in  the  menstruum. 

Other  solutions  were  then  examined.  Calcium 
chloride  in  alcohol,  and  sulphur  in  carbon  disul- 
phide,  showed  no  indications  of  precipitation  at 
temperatures  above  the  critical  points  of  the 
solvents.  The  blue  solution  of  cobaltous  chloride 
in  alcohol  preserved  its  color  at  temperatures  far 
above  the  critical  point  of  alcohol.  The  absorption 
spectrum  showed  no  change  on  passing  through 
the  critical  point.  The  authors  accepted  these 
results  as  evidence  of  the  solubility  of  solids  in 
gases,  and  of  the  perfect  continuity  of  the  gaseous 
and  liquid  states.  Ramsay  considers  the  last  of 
these  experiments  as  an  evidence  that  the  liquid 
state  persists  beyond  the  critical  point.  He  says  : 
"  Messrs.  Hannay  and  Hogarth  found  that  the 
absorption  spectrum  of  colored  salts  remains  un- 


90  LIQUEFACTION   OF   GASES 

altered  even  when  the  liquid  in  which  they  are 
dissolved  loses  its  meniscus.  Surely  no  clearer 
proof  is  needed  to  show  that  the  solids  are  not 
present  as  gases,  but  are  simply  solutions  in  a 
liquid  medium."  l 

Ramsay2  has  determined  the  condition  of  a 
fluorescent  solution  at  temperatures  above  the 
critical  point  of  the  solvent.  Eosine  in  alcoholic 
solution  failed  to  show  the  phenomenon  of  fluo- 
rescence after  the  meniscus  had  disappeared. 
The  author  showed  that  benzene,  at  temperatures 
slightly  above  the  critical  point,  expands  and  con- 
tracts, with  regard  to  pressure,  approximately  the 
same  as  a  liquid.  The  gaseous  state,  he  thinks, 
depends  entirely  upon  the  mean  velocity  of  the 
molecules  and  not  upon  the  mean  free  path.  He 
considered  a  gas  as  a  substance  consisting  of  simple 
molecules,  and  a  liquid  as  a  substance  consisting 
of  aggregates  -of  gaseous  molecules.  Above  the 
critical  point,  he  says,  a  substance  may  be  wholly 
liquid  or  gas,  depending  upon  the  pressure. 

Three  years  later  Jamiu3  announced  a  similar 
theory.  He  saw  no  reason  why  the  liquid  state 
should  cease  at  the  critical  point.  He  says :  "  I 
believe  that  gases  are  liquefiable  at  any  tem- 
perature when  the  pressure  is  sufficient,  but  that 

1  Proc.  Roy.  Soc.,  30,  p.  327.         2  Ibid.,  31,  p.  194. 
»  Phil.  Mag.  [5],  1 6,  p.  71,  1883. 


CONTINUITY   OF   STATE  91 

an  unperceived  circumstance  has  prevented  the 
liquefaction  from  being  seen."  He  looked  upon 
the  disappearance  of  the  meniscus  only  as  an  evi- 
dence that  the  density  of  the  liquid  was  equal  to 
that  of  the  vapor,  —  a  condition  which  could  be 
brought  about  by  means  of  pressure  alone.  In 
support  of  this  theory  the  following  experiment 
of  Cailletet 1  is  quoted :  A  mixture  of  one  part  of 
air  and  five  parts  of  carbonic  acid  was  compressed 
until  a  portion  of  the  latter  gas  was  liquefied.  The 
pressure  was  then  increased  to  200  atmospheres, 
when  the  meniscus  disappeared.  Jamin  explains 
this  phenomenon  on  the  assumption  that  the  den- 
sity of  the  gas  at  that  pressure  was  equal  to  that  of 
the  liquid. 

Cailletet  and  Colardeau2  have  also  endeavored 
to  prove  that  the  liquid  state  persists  at  tempera- 
tures above  the  critical  point.  They  experimented 
with  a  solution  of  iodine  in  liquid  carbonic  acid. 
The  colored  solution  was  heated,  in  a  closed  glass 
tube,  to  the  critical  point  of  the  solvent.  After 
the  meniscus  disappeared  the  portion  of  the  tube 
which  had  contained  the  liquid  remained  colored, 
while  the  upper  portion  was  colorless.  The  ab- 
sorption spectrum  of  the  substance  in  this  condi- 
tion showed  that  the  iodine  existed  in  solution,  and 

1  Compt.  rend.,  90,  p.  210,  1880. 

2  Ann.  de  Chim.  et  de  Phys.  [6],  18,  p.  269,  1889. 


92  LIQUEFACTION   OF   GASES 

not  as  a  vapor.  The  authors  concluded  then  that 
the  liquid  state  still  persisted  in  the  lower  portion 
of  the  tube.  Villard,1  however,  has  shown  that 
under  certain  conditions  iodine  is  soluble  in  gaseous 
carbonic  acid,  and  that  this  does  not  serve  as  a  test 
for  the  liquid  state. 

The  theory  that  the  critical  point  is  the  limit  of 
the  liquid  state  has  been  ably  defended  by  Hannay. 
Reference  has  already  been  made  to  his  work  on 
the  solubility  of  solids  in  gases.  Later  he  investi- 
gated the  phenomenon  of  capillarity  2  for  carbonic 
acid,  ammonia,  sulphurous  acid,  nitrous  oxide,  car- 
bon disulphide,  chlorine,  and  various  alcohols,  and 
found  that  capillarity  disappears  at  or  near  the 
critical  point.3  He  looked  upon  the  solvent  power 
of  a  gas  as  depending  upon  two  conditions,  the 
molecular  closeness  and  the  vis  viva.  At  con- 
stant density,  he  says,  the  solvent  power  increases 
with  the  kinetic  energy  of  the  molecules.  This 
statement,  however,  requires  some  modification. 
Altschul4  has  carefully  studied  the  influence  of  tem- 
perature on  the  solvent  power  of  a  gas.  He  filled 
a  strong  glass  tube  with  a  solution  of  I  gram 


1  Ann.  de  Chim.  et  de  P/iys.,  10,  p.  387,  1897. 

2  Proc.  Roy.  Soc.,  30,  p.  478,  1880. 

8  Similar  observations  were  also  made  by  Clark.    Proc.  Phys.  Soc.t 
Lond.,  4,  p.  41. 

*  Zeit.  compr.  undfliiss.  Case,  I,  p.  207,  1897. 


CONTINUITY   OF   STATE  93 

of  potassium  iodide  in  150  grams  of  alcohol,  and 
carefully  heated  the  substance  to  the  critical 
point  of  the  solvent.  At  this  temperature  the 
substance  remained  in  solution,  but  when  gradu- 
ally heated  to  a  temperature  of  about  356°  a  por- 
tion of  the  tube  became  filled  with  very  fine 
glistening  crystals,  which  could  be  seen  with  the 
naked  eye.  These  crystals  did  not  settle  to  the 
bottom,  but  floated  about  throughout  the  whole 
space  of  the  tube.  From  this  observation,  it  is 
evident  that  the  statement  of  Hannay  that,  "re- 
taining the  volume  the  same,  the  higher  the  tem- 
perature the  greater  the  solvent  power  of  K 
a  gas,"  is  true  only  within  certain  limits. 

Hannay  also  made  use  of  an  entirely 
different  method  for  studying  the  condi- 
tion of  a  fluid  at  the  critical  point.     The 
apparatus   employed   is   shown  in 
figure  1 6.     The  liquid  was  en- 
closed in  the  upper  part 
of   the   tube   A    by 
means  of  the  mer- 
cury B.     The  lower 

^>^^  FIG.  16. 

part  of  the  appa- 
ratus C  was  filled  with  nitrogen.  By  compressing 
the  mercury,  and  gently  tapping  the  tube,  a  small 
bubble  of  the  gas  could  be  made  to  pass  up 
through  the  column  of  mercury  into  the  liquid. 


94  LIQUEFACTION   OF   GASES 

At  temperatures  below  the  critical  point,  the 
bubble  of  nitrogen  showed  a  distinct  meniscus, 
and  passed  up  through  the  column  of  liquid.  At 
temperatures  above  the  critical  point,  the  bubble 
diffused  immediately  throughout  the  whole  space. 
Hannay  looked  upon  this  experiment  as  decisive 
evidence  that  the  liquid  state  ceases  at  the  critical 
temperature.  He  says  :  "  There  can  be  no  liquid 
above  the  critical  point,  as  this  is  the  termination 
of  all  properties  which  distinguish  a  liquid  from  a 
gas." 

We  come  now  to  the  question  originally  asked 
by  Andrews.  "What  is  the  condition  of  matter, 
at  temperatures  slightly  above  the  critical  point?" 
Does  it  belong  to  the  liquid,  or  the  gaseous  state  ? 
The  answer  to  this  question  depends  entirely 
upon  the  definitions  of  the  terms  liquid  and  gas. 
Hannay l  suggests  four  states  of  matter,  —  the 
gas,  vapor,  liquid,  and  solid.  The  vapor,  he  says, 
is  a  distinct  state  of  matter.  The  fact,  however, 
that  some  of  the  properties  of  vapors  differ  from 
those  of  gases  under  ordinary  conditions,  is  not 
necessarily  an  evidence  of  a  different  state  of 
matter,  in  the  sense  in  which  that  term  is  usually 
employed.  Crookes2  has  shown  that  the  proper- 
ties of  gases  under  extremely  low  pressures  differ 

1  Proc.  Roy.  Sot.,  31,  p.  520. 

2  Ibid.,  30,  p.  469,  1880. 


CONTINUITY   OF   STATE  95 

essentially  from  those  of  gases  under  the  ordinary 
pressure,  and  he  has  suggested  the  term  radiant 
matter  for  such  conditions.  Three  states  of 
matter,  then,  apart  from  the  liquid  and  solid,  have 
already  been  suggested,  —  namely,  the  vapor,  the 
gas,  and  radiant  matter.  It  is  evident,  from  the 
above  suggestions,  that  the  state  which  shall  be 
assigned  to  matter  under  definite  conditions  de- 
pends entirely  upon  the  definitions  of  the  various 
terms.  If  we  limit  the  states  of  matter  to  the 
solid,  liquid,  and  gas,  which  is  probably  advisable, 
and  accept  the  ordinary  definitions,  —  namely,  that 
a  gas  has  neither  form  nor  volume,  but  tends  to 
expand  indefinitely,  and  that  a  liquid  has  a  defi- 
nite volume,  but  assumes  the  form  of  the  vessel 
in  which  it  is  contained,  then  it  seems  that  a  fluid 
above  the  critical  point  belongs  to  the  gaseous 
state.  Matter  in  that  condition  tends  to  expand 
indefinitely  without  showing  any  signs  of  ebulli- 
tion. If  a  small  bubble  of  an  indifferent  gas  is 
allowed  to  enter  the  fluid,  it  shows  no  meniscus, 
but  diffuses  imperceptibly  throughout  the  whole 
space. 

The  gaseous  and  liquid  states,  however,  gradu- 
ally approach  each  other  at  the  critical  point.  The 
change  from  a  gas  to  a  liquid  at  this  point  seems 
to  be  a  continuous  process,  and  shows  no  abrupt 
evolution  of  heat.  The  intimate  relation  which 


96  LIQUEFACTION   OF   GASES 

exists  between  the  two  states  has  been  admirably 
expressed  by  Andrews.  He  says  :  "  The  ordinary 
gaseous  and  ordinary  liquid  states  of  matter  may 
be  made  to  pass  into  one  another  by  a  series  of 
gradations  so  gentle  that  the  passage  shall  nowhere 
present  any  interruption  or  breach  of  continuity. 
From  carbonic  acid  as  a  perfect  gas  to  carbonic 
acid  as  a  perfect  liquid,  the  transition  we  have 
seen  may  be  accomplished  by  a  continuous  pro- 
cess, and  the  gas  and  liquid  are  only  distant  stages 
of  a  long  series  of  continuous  physical  changes." 

SECTION   III 

Relation  between  the  Gaseous  and  Liquid  States,  as 
expressed  by  the  Equation  of  Van  der  Waals 

According  to  Boyle's  law  (p.  7),  the  product  of 
the  pressure  and  volume  of  a  gas  is  a  constant 
quantity.  This  relation  is  expressed  by  the 

equation, 

pv  =  c. 

According  to  the  law  of  Charles-Gay  Lussac  (p.  10), 
the  volume  v±  of  a  gas  at  any  temperature  t,  and 
under  the  constant  /0,  is  given  by  the  equation, 


where  VQ  is  the  volume  of  the  gas  at  o°,  and  a  is 
the  coefficient  of  expansion  (= 


EQUATION   OF   VAN   DER  WAALS  97 

If  the  pressure  in  the  last  equation  should  change 
from  /0  to  any  pressure  /,  the  resulting  volume  #, 
according  to  Boyle's  law,  is, 


hence,  pv  =  p^(\  +  at). 

If  T  represents  the  absolute  temperature,  then 
t—T—  273.  The  coefficient  of  expansion  a  being 
equal  to  ^  J3>  we  have, 


or,  pv 

273 

The  expression  /0?>0  represents  the  product  of  the 
pressure  and  volume  at  o°  and  760  mm.  pressure  ; 


hence,  is   a   constant.     Calling  this  term  R, 

we  have  pv=RT.  I 

This  is  the  equation  usually  employed  to  express 
the  relation  of  the  pressure  and  volume  to  the 
temperature  of  a  gas.  It  represents  a  combina- 
tion of  the  law  of  Boyle  with  that  of  Charles  -Gay 
Lussac. 

Reference  has  already  been  made  to  the  fact 
that  gases  under  high  pressures  deviate  from 
Boyle's  law  (p.  65).  The  most  elaborate  series  of 


93  LIQUEFACTION   OF   GASES 

experiments  in  this  direction  is  that  of  Amagat.1 
He  took  into  account  both  pressure  and  tempera- 
ture, and  hence  his  results  apply  directly  to 
equation  I. 

The  results  obtained  by  Amagat  are  represented 
by  the  curves  in  figures  17,  18,  19,  and  20.     Fig- 


£0      -4O       <SO      <30        100      120      I4O      /60      I8O      £00     ISO 
FIG.    I7. 


ure  17  shows  the  compressibility  of  hydrogen. 
The  abscissas  represent  the  pressures  in  atmos- 
pheres, while  the  ordinates  represent  the  corre- 
sponding values  of  the  product  pv.  If  the  equation 
pv  =  R  T  should  remain  true  under  all  conditions, 
the  curves  would  become  straight  lines  parallel  to 


1  Ann.  de   Chim.  et  de  Phys.  [4],  29;    [5],  23,  p.  358;    Compt. 
rend.,  73,  p.  183;   75,  p.  479. 


EQUATION   OF  VAN   DER  WAALS 


99 


the  axis  of  abscissas.  The  curves  for  hydrogen 
are  approximately  straight  lines  under  the  condi- 
tions of  the  experiments,  but  the  value  of  pv  in- 
creases, after  a  certain  point  has  been  reached, 
with  increasing  pressure. 

The  curves  for  nitrogen  are  shown  in  figure  18. 
In  this  case  the  product  of  pv  decreases  slightly 


120     140     J6O    1QO     SOO    £20    £-40 

FIG.  1  8. 


ZOO  3OO    JKO 


at  first,  and  then  increases  with  increasing  press- 
ure. As  the  temperature  is  lowered  the  curves 
for  both  hydrogen  and  nitrogen  show  greater 
divergences  from  a  straight  line. 

Figure  19  represents  the  curves  for  ethylene. 
In  this  case  the  divergence  from  a  straight  line 
becomes  more  pronounced.  The  value  of  pv  de- 
creases rapidly  at  first,  and  then  increases.  The 


100 


LIQUEFACTION    OF   GASES 


change  in  the  direction  of  the  curve  becomes  more 
abrupt  as  the  temperature  approaches  the  critical 
point.  The  form  of  the  curves  for  extremely  high 


\ 


\ 


\ 


to        40       OO       nr. 


140    .if)!)     tna      £20     no    ttn     fen    Joo 


FIG.  19. 


temperatures  would  be  similar  to  those  of  nitrogen 
and  hydrogen. 

The  curves  for  carbonic  acid  (Fig.  20)  are  very 


EQUATION   OF   VAN 


similar  to  those  for  ethylene.  Near  the  critical 
point  the  change  in  the  direction  of  the  curve 
becomes  very  abrupt.  The  compressibility  at  35°, 


\ 


\ 


\\ 


\ 


\ 


\ 


ISO       }40       '60       IQO 

FIG.  20. 


SAO    JOO     320 


and  above  80  atmospheres    pressure,  is   approxi- 
mately the  same  as  for  liquid  carbonic  acid. 

In  1888  Amagat1  extended  his  observations  on 

1  Compt.  rend.t  107,  p.  523. 


K-V^V"?  J  LIQUEFACTION   OF  GASES 

air,  nitrogen,  oxygen,  and  hydrogen  to  pressures 
as  high  as  3000  atmospheres,  and  found  that  the 
compressibility  of  these  gases  under  extremely 
high  pressures  is  approximately  the  same  as  for 
liquids.  The  density  of  oxygen  at  a  pressure  of 
3000  atmospheres  was  found  to  be  greater  than 
that  of  water. 

Reference  might  be  made  to  other  experiments 
of  Amagat  in  this  field,  as  well  as  to  those  of 
other  investigators.  The  preceding  examples,  how- 
ever, are  sufficient  to  show  that  the  equation  pv 
=  RT,  while  approximately  true  under  certain 
conditions  of  temperature  and  pressure,  cannot 
be  applied  to  gases  under  all  conditions. 

Numerous  attempts  have  been  made  to  deduce 
a  formula  which  will  express  the  mutual  relation 
of  the  pressure,  volume,  and  temperature  of  gases 
under  all  conditions.  The  most  complete  equa- 
tions are  those  of  Van  der  Waals  and  Clausius. 
Both  of  these  equations  are  based  upon  the  kinetic 
theory  of  gases,  according  to  which  the  molecules 
of  all  gases  are  in  a  state  of  motion.  The  press- 
ure of  a  gas,  according  to  this  theory,  is  due  to 
molecular  impacts  against  the  walls  of  the  con- 
taining vessel. 

The  kinetic  theory  of  gases  involves  the  assump- 
tion that  gaseous  molecules  are  perfectly  elastic. 
Granting  this  assumption,  and  supposing  each 


EQUATION   OF   VAN   DER  WAALS  103 

molecule,  between  any  two  successive  collisions 
against  other  molecules  or  against  the  walls  of  the 
vessel,  to  move  in  a  straight  line,  then  the  pressure 
of  a  gas,  in  terms  of  molecular  velocity,  etc.,  can 
be  calculated.  Some  of  the  calculations  in  this 
direction  are  very  elaborate,  and  involve  higher 
mathematics.  The  more  elementary  calculation, 
which  can  be  found  in  numerous  text-books,  is 
sufficient  for  the  present  purpose. 

Suppose  the  gas  to  be  contained  in  a  cube,  the 
side  of  which  is  /  units  in  length.  Let  n  represent 
the  number  of  molecules,  each  of  which  is  moving 
with  the  velocity  #,  and  m  the  mass  of  each  mole- 
cule. The  velocity  u  of  a  molecule  moving  in  any 
direction  can  be  resolved  into  the  three  compo- 
nents, x,  y,  and  zt  at  right  angles  respectively  to 
three  sides  of  the  cube,  provided  the  relation 
x1  +  y2  +  ^2  =  ^2  is  preserved. 

Suppose  we  consider  a  single  molecule  moving 
with  the  velocity  x  perpendicular  to  one  side  of 
the  cube.  The  molecule,  being  perfectly  elastic, 
rebounds  from  the  wall  of  the  vessel  with  a  ve- 
locity equal  to  that  with  which  it  approaches.  Con- 
sequently the  impulse  given  to  the  wall  by  each 
collision  will  be  equal  to  2  mx,  —  i.e.  twice  the 
momentum  of  the  molecule.  The  collision  against 

the  two  parallel  faces  of  the  cube  will  take  place  - 


i64  LIQUEFACTION  OF  GASES 

times  per  unit  of  time.  Hence,  the  total  action  of 
a  molecule  per  unit  of  time  is  — - — .  The  same 

is  true  for  the  other  two  components,  and  we  have, 
for  the  total  action  of  a  molecule  against  all  sides 
of  the  vessel  per  unit  of  time,  the  value, 


The  total  impulse,  then,  of  all  the  molecules  per 


o   7/7  //7/ 

unit  of  time  is  equal  to  --  —  .     This  value  rep- 

resents the  total  pressure  on  all  sides  of  the  vessel. 
Dividing  this  expression  by  the  area  of  the  cube 
(6/2),  we  obtain  the  pressure/  per  unit  of  area; 

imgm  p  =  2  y***2.     The  volume  of   the   vessel,   of 

course,  is  equal  to  /3.  Representing  this  by  v, 
and  simplifying,  we  have 


or 

pv=  §•;«#—. 


According  to  this  expression,  the  product  of  the 
pressure  and  volume  of  a  gas  is  equal  to  two-thirds 
of  the  kinetic  energy  of  the  molecules.  Inasmuch 
as  the  temperature  of  a  gas  varies  directly  with 


EQUATION   OF   VAN   DER  WAALS  105 

the  kinetic  energy  of  the  molecules,  this  equation 
is  similar  in  every  respect  to  the  equation, 


The  above  calculations  are  based  upon  the  as- 
sumption that  the  molecules  are  free  to  move 
throughout  the  entire  space  of  the  containing 
vessel,  and  that  the  mutual  attraction  between  the 
molecules  is  inappreciable.  It  is  evident,  how- 
ever, that  the  molecules  are  free  to  move  only  in 
the  space  which  is  not  occupied  by  the  molecules 
themselves.  A  correction  must  be  made,  there- 
fore, for  the  actual  volume  of  the  molecules.  At 
low  pressures  this  correction  is  very  small,  but  at 
high  pressures,  where  the  molecules  are  crowded 
together  more  closely,  it  becomes  appreciable.  At 
high  pressures,  also,  the  mutual  attraction  between 
the  molecules  must  be  taken  into  account. 

In  the  equation  developed  by  Van  der  Waals  l 
the  influence  due  to  the  actual  volumes  of  the 
molecules,  and  to  the  mutual  attraction  between 
the  molecules,  is  taken  into  consideration.  The 
complete  equation  is 


in  which  />,  v,  R,  and  T  represent  the  same  values 

1  Die  Continuit'dt  des  gasformigen  und  fliissigen  Zustandes. 


io6  LIQUEFACTION   OF   GASES 

as  in  equation  I  (p.  97),  a  is  a  function  of  the 
mutual  attraction  between  the  molecules,  and  b  is 
proportional  to  the  actual  space  occupied  by  the 
molecules. 

The  development  of  this  equation  represents  an 
elaborate  mathematical  calculation.  For  the  pres- 
ent purpose,  however,  we  will  consider  only  the 
application.  Taking  the  atmospheric  pressure  as 
unit  pressure,  and  the  volume  of  one  gram  of  gas 
at  o°  and  a  pressure  of  one  atmosphere  as  unit 
volume,  Van  der  Waals  calculated  the  values  of  a 
and  b,  from  the  compressibility  of  carbonic  acid 
gas,  and  found  them  to  be  0.00874  and  0.0023  re" 
spectively.  Substituting  these  values,  we  have 

w_  0.0023)  =RT. 

Placing  p  and  v  each  equal  to  unity,  the  corre- 
sponding temperature  is  o°,  or  7^=273;  and 

hence, 

R  =  1.00646 

273 

If  a  and  b  remain  constant  under  all  conditions,  we 
have  as  a  general  equation  for  carbonic  acid 


The  values  of  /  and  v  obtained  from  this  equa- 
tion for  different  values  of  T  are  represented  by 


EQUATION   OF   VAN   DER  WAALS 


107 


the  curves1  in  figure  21.  The  volumes  are  rep- 
resented by  abscissas,  and  the  corresponding  press- 
ures by  ordinates.  The  curve  AD  corresponds  to 


FIG.  21. 


a  temperature  of    13°.!.      The  curve,   instead  of 
passing  from  B  to   C  in  a  straight  line,  as  was 


1  Ostvvald,  Outlines  of  Gen.  Chem.,  p.  86. 


io8  LIQUEFACTION   OF   GASES 

observed  by  Andrews  (p.  78),  is  continuous,  and 
passes  through  the  points  a  and  7.  In  1871 
J.  Thomson1  suggested  that  the  curves  given  by 
Andrews  could  probably  be  obtained  as  continuous 
curves.  The  curves  represented  in  figure  21  are 
very  similar  to  those  suggested  by  Thomson.  In 
each  of  the  curves  I,  2,  and  3  it  will  be  noticed  that 
there  are  three  volumes  corresponding  to  one  press- 
ure. In  curve  I  the  three  volumes  corresponding 
to  a  single  pressure  occur  only  between  the  limits 
of  pressure  represented  by  y  and  a.  As  the  tem- 
perature increases,  the  three  points  on  the  curves 
representing  these  three  different  volumes  gradu- 
ally approach  each  other,  and  finally  meet  at  the 
point  k. 

The  point  k,  where  the  three  volumes  become 
equal  to  each  other,  was  called  by  Van  der  Waals 
the  critical  point.  For  carbonic  acid  .this  point 
corresponds  to  a  temperature  of  32°. 5.  Above 
this  temperature  there  is  but  one  volume  corre- 
sponding to  a  definite  pressure.  This  tempera- 
ture is  about  one  and  a  half  degrees  higher  than 
the  critical  temperature  obtained  experimentally 
by  Andrews.  The  pressure  corresponding  to  the 
point  k  represents  the  critical  pressure.  In  the 
case  of  carbonic  acid  the  calculated  value  is  61 

1  Proc.  Roy.  Soc.,  1871. 


EQUATION   OF   VAN   DER   WAALS  109 

atmospheres,  while  the  experiments  of  Andrews 
show  a  value  of  about  70  atmospheres.  The 
volume  corresponding  to  the  point  k  represents 
the  critical  volume. 

The  same  results  may  be  obtained  by  solving 
the  equation  algebraically.  If  the  equation  be 
arranged  according  to  the  descending  powers  of 
v,  we  have 

o      (y   .  RT\  »  .  a        ab         l 
tr  —  (b  +  —  -}v*  +  -v  --  =  o.1 

\PJPP 

This  equation  is  of  the  third  degree  with  respect 
to  v,  and,  of  course,  has  three  roots.  A  solution 
of  the  equation  will  show  that  the  three  roots  are 
real,  or  that  one  is  real  and  the  other  two  imagi- 
nary. That  is,  for  any  pressure  there  are  either 
three  values  or  one  value  of  v. 

This  fact  is  also  shown  by  the  graphic  represen- 
tation in  figure  2  1  .  These  curves  show  that,  within 
a  certain  interval  of  pressure  for  each  temperature 
below  32°.  5,  there  are  three  corresponding  values 

1  The  equation  as  given  by  Van  der  Waals  is 

'+*)('  "*)('+  « 


In  this  formula,  we  have,  instead  of  R,  the  expression  (  I  -f  a)  (  I  —  b}  . 
This  value  is  obtained  by  placing  p  and  v  each  equal  to  unity  in 
the  original  equation  of  Van  der  Waals.  Substituting  R  for  the 
expression  (i  +  ar)(i  —  £),  and  introducing  the  absolute  tempera- 
ture T,  we  obtain  the  equation  given  above, 


/ 

—  ( 

\ 


no  LIQUEFACTION   OF^   GASES 

for  the  volume;  while  above  32°.  5,  each  pressure 
corresponds  to  a  definite  volume.  At  the  critical 
point  /£,  the  three  volumes  are  equal  to  each  other. 
If  we  assume,  then,  that  at  the  critical  point, 
the  three  values  of  v,  or  the  three  roots  of  the 
equation 

RT\   9  ,  a        ab 

\ir  +  -v  --  =  o 
pjpp 

are  each  equal  to  <£,  the  value  of  $  must  be  such 
that 

•       o  -\-  RT         .9      ci          JJQ      ttb 
3<#>=-Zr  —  ,    34>2=-,    and<£3  =  —  . 
P  P  P 

Simplifying  these  expressions,  and  representing 
the  critical  temperature  by  0,  and  the  critical  press- 
ure by  TT,  we  obtain, 

<j>  —  3  b  =  critical  volume. 

TT  =    a  0  =  critical  pressure. 
27  bz 

0  =  --  -—  =  critical  temperature. 
27  Rb 

Having  once  determined  the  values  of  a  and  b 
for  a  gas,  the  critical  constants  can  be  calculated 
from  the  above  formulas.  The  critical  constants 
of  carbonic  acid  calculated  in  this  manner,  and  the 
corresponding  values  obtained  experimentally  by 
Andrews,  are  as  follows  :  — 


EQUATION   OF   VAN   DER   WAALS  in 


Calculated 

Experimental 

Critical  temperature     .     .     . 
Critical  pressure      .... 
Critical  volume  

32°-5 
61  atm. 
o  0069 

3o°-92 
70  atm. 
0.0066 

The  equation  of  Van  der  Waals  applies  to  a 
homogeneous  gas  or  a  homogeneous  liquid.  It 
does  not,  however,  apply  to  a  liquid  and  its  vapor 
in  mutual  contact.  During  the  last  twenty  years 
this  equation  has  been  the  subject  of  considerable 
discussion.  The  very  elaborate  series  of  experi- 
ments by  Young  1  show  that  the  generalizations  of 
Van  der  Waals  can  be  regarded  only  as  approxi- 
mations. 

In  1880  Clausius2  called  attention  to  some  devia- 
tions from  the  equation  of  Van  der  Waals.  He 
regarded  the  assumption  of  Van  der  Waals,  that 
the  mutual  attraction  of  the  molecules  is  indepen- 
dent of  the  temperature,  and  is  a  function  only  of 
the  volume,  as  true  only  for  a  perfect  gas.  The 
assumption  that  the  mutual  attraction  of  the  mole- 
cules is  inversely  proportional  to  the  square  of  the 
volume  was  regarded  by  Clausius  only  as  a  close 
approximation  under  certain  conditions.  Clausius 
finally  suggested  the  following  equation  to  express 

1  Proc.  Phys.  Soc.,  Lond.,  p.  233,  1897. 

2  Phil.  Mag.  [5],  9,  p.  393. 


112  LIQUEFACTION   OF   GASES 

the  relation  of  the  pressure  and  volume  to  the 
temperature  of  a  gas :  — 

.  _  r>    T c 

P'       v-a      T(v-0yf 

in  which  R,  c,  a,  and  0  are  constants.  In  some 
respects  this  equation  is  a  closer  approximation 
than  that  of  Van  der  Waals.  In  1882  Sarrau1 
investigated  this  equation  very  thoroughly  with 
reference  to  the  experimental  results  obtained  by 
Amagat.  He  found  that,  in  the  case  of  hydrogen 
and  nitrogen,  the  equation  expresses  very  closely 
the  actual  relation  of  the  pressure  and  volume  to 
the  temperature.  With  certain  other  gases,  how- 
ever, some  deviations  were  observed. 

From  the  experimental  results  it  is  evident  that 
the  equations  of  Van  der  Waals  and  Clausius,  as 
well  as  similar  equations  of  other  experimenters, 
can  be  regarded  only  as  close  approximations.2 
Inasmuch  as  all  of  these  equations  are  based  upon 
the  kinetic  theory  of  gases,  it  may  be  remarked 
that  within  recent  years  considerable  opposition 
has  been  offered  against  this  theory. 

1  Compt.  rend.,  94,  pp.  639,  718,  and  845. 

2  As  further  reference  to  this  subject   see,  among  others,  Ran- 
kine,  J^rans.  Roy.   Soc.,  1854,  p.  336;  Joule  and  Thomson,  ibid., 
1862,  p.  579;   Recknagel,  Pogg.  Ann.,  145,  p.  469,   1872;   Him, 
Theorie  Mechanique  de  la   Chaleur,  3d  ed.,  II,  p.  21 1 ;   Amagat, 
Ann.  de   Chim.  et  de  Phys.  [5],  28,  p.  500,  1883;    and  Zeit.  fur 
Compr.  und  fl'iiss.    Case,  2,  p.   178,   1898;    Violi,  Phil.  Mag.,  27, 
p.  527,  1889;   J-  Traube,  Wied.  Ann.,  61,  2,  pp.  380-400,  1897. 


CHAPTER   IV 

LIQUEFACTION  OF  THE  SO-CALLED  PERMANENT 
GASES 

SECTION  I 

"THE  meeting  of  the  French  Academy  on  the 
twenty-fourth  of  December,  1877,  was  a  memor- 
able one.  On  that  day  the  members  were  told 
that  Cailletet  had  succeeded  in  liquefying  both 
oxygen  and  carbon  monoxide  at  his  works  at 
Chatillon-sur-Seine,  and  that  the  former  gas  had 
also  been  liquefied  by  Raoul  Pictet  in  Geneva." 
The  following  letter,1  addressed  by  Cailletet  to 
Sainte-Claire  Deville,  was  read  by  Dumas  :  — 

"  I  have  to  tell  you  first,  and  without  losing  a  moment, 
that  I  have  just  this  day  liquefied  oxygen  and  carbon 
monoxide. 

"  I  am,  perhaps,  doing  wrong  to  say  liquefied,  for  at  the 
temperature  obtained  by  the  evaporation  of  sulphurous 
acid,  about  —  29°,  and  at  a  pressure  of  300  atmospheres, 
I  see  no  liquid,  but  a  mist  so  dense  that  I  infer  the  pres- 
ence of  a  vapor  very  near  its  point  of  liquefaction. 

"  I  write  to-day  to  M.  Deleuil  for  some  protoxide  of 
nitrogen,  by  means  of  which  I  shall  be  able,  without  doubt, 
to  see  oxygen  and  carbon  monoxide  flow. 

1  Compt.  rend.,  85,  p.  1217. 


U4  LIQUEFACTION   OF   GASES 

"  P.  S.  —  I  have  just  made  an  experiment  which  sets 
my  mind  greatly  at  ease.  I  compressed  hydrogen  to 
300  atmospheres,  and  after  cooling  down  to  —  28°,  I  re- 
leased it  suddenly.  There  was  not  a  trace  of  mist  in  the 
tube.  My  gases,  carbon  monoxide  and  oxygen,  are 
therefore  about  to  liquefy,  as  this  mist  is  produced  only 
with  vapors  which  are  on  the  verge  of  liquefaction.  The 
prediction  of  M.  Berthelot  has  been  completely  realized. 

"  Louis  CAILLETET. 
"December  2,  1877." 

Deville  added  also  that  Cailletet  had  successfully 
repeated  his  experiments  on  the  condensation  of 
oxygen,  on  Sunday,  December  sixteenth,  in  the 
laboratory  of  the  Normal  School. 

The  following  telegram l  was  then  read  :  — 

"  GENEVA,  December  22. 

"  To-day  I  liquefied  oxygen  at  a  pressure  of  320  atmos- 
pheres, and  a  temperature  of  —  140°,  obtained  by  means 
of  sulphurous  and  carbonic  acids. 
"  Signed, 

"  RAOUL  PICTET." 

During  the  session  of  the  Academy  a  second 
telegram  2  was  received  from  Pictet. 

"GENEVA,  December  24,  4.15  P.M. 

"A  second  experiment,  performed  before  numerous 
assistants,  has  thoroughly  confirmed  the  results  which  I 
communicated  to  M.  Dumas  last  Saturday. 

"  PICTET." 

1  Compt.  rend.,  85,  p.  1214.  '2  Ibid.,  p.  1220. 


EXPERIMENTS   OF  CAILLETET  115 

The  researches  of  Andrews  had  already  shown 
that  all  gases  under  the  proper  conditions  of  tem- 
perature and  pressure  would  pass  into  the  liquid 
state.  The  experimental  evidence,  however,  for 
the  so-called  permanent  gases,  was  left  for  these 
two  simultaneous,  but  independent  experimenters. 
Roscoe  and  Schorlemmer,  in  their  account  of  these 
observations,  say :  "  It  is  difficult,  on  reading  the 
descriptions  of  these  experiments,  to  know  which 
to  admire  most,  the  ingenious  and  well-adapted 
arrangement  of  the  apparatus  employed  by  Pictet, 
or  the  singular  simplicity  of  that  used  by  Cailletet. 
The  latter  gentleman  is  one  of  the  greatest  of 
French  ironmasters,  whilst  the  former  is  largely 
engaged  as  a  manufacturer  of  ice-making  machin- 
ery, and  the  experience  and  practical  knowledge 
gained  by  each  in  his  own  profession  have  materi- 
ally assisted  to  bring  about  one  of  the  most  inter- 
esting results  in  the  annals  of  scientific  discovery." 

EXPERIMENTS  OF  CAILLETET 

Previous  to  the  experiments  with  oxygen,  Caille- 
tet succeeded  in  liquefying  a  number  of  gases. 
He  condensed  acetylene 1  to  a  colorless,  extremely 
mobile  liquid,  and  found  its  vapor-pressure  to  be 
48  atmospheres  at  a  temperature  of  i°,  and  103 

1  Compt.  rend.,  85,  p.  851. 


LIQUEFACTION   OF   GASES 


atmospheres  at  31°.  He  also  liquefied  nitric  oxide 
and  methane.1  The  former  gas  condensed  at  a 
temperature  of  —  11°,  when  subjected  to  a  press- 
ure of  104  atmospheres.  At  a  temperature  of 
+  8°  there  was  no  sign  of  liquefaction,  even 

with  a  pressure  of  270 
atmospheres.  He  con- 
cluded that  the  critical 
temperature  was  be- 
tween -f  8  and  —  1 1°. 
The  methane  was  ob- 
tained only  in  the  form 
of  a  mist.  The  pure 
gas  was  subjected  to 
a  pressure  of  180  at- 
mospheres, and  a  tem- 
perature of  7°.  By 
releasing  the  pressure 
suddenly,  the  gas  was 
condensed  to  a  fine 
mist.  These  results 
were  communicated  to 
the  French  Academy 
by  Berthelot,  who  stated 

at  the  same  meeting  that  oxygen  and  similar  gases 
could  probably  be  liquefied  by  the  new  method 
which  had  been  introduced  by  Cailletet. 


77 


FIG.  22. 


1  Compt.  rend,,  85,  p.  1016. 


EXPERIMENTS    OF   CAILLETET  117 

The  apparatus1  employed  by  Cailletet  in  the 
liquefaction  of  oxygen  and  carbon  monoxide  was 
similar  to  that  used  in  the  previous  experiments. 
A  longitudinal  section  of  the  condensing  apparatus 
is  shown  in  figure  22.  The  glass  tube  TT  is  en- 
tirely filled  with  the  gas  to  be  compressed.  This 
tube  can  be  removed  from  the  apparatus  as  shown 
in  figure  23.  When  the  air  in  the  tube  has  been 
completely  displaced  by  the  gas,  the  upper  end  of 


T. 


FIG.  23. 

the  tube  is  hermetically  sealed.  The  lower  end  is 
closed  with  the  finger,  and  the  tube  introduced 
into  the  strong,  wrought-iron  cylinder  B,  which  is 
partially  filled  with  mercury.  The  tube  is  fastened 
in  the  receiver  by  means  of  the  bronze  screw  A. 
The  upper  portion  of  the  tube  is  surrounded  by  a 
glass  cylinder  M,  containing  liquid  nitrous  oxide, 
which  in  turn  is  surrounded  by  a  safety  bell-jar 
C.  n  and  n'  represent  gauges  for  measuring  the 
pressure. 

The  method  of  operation  is  very  simple.     Water 
is  forced  through  the  tube  //  into  the  cylinder  B, 

1  Ann.  de  Chim.  et  de  Phys.  [5],  15,  p.  132. 


n8  LIQUEFACTION   OF   GASES 

by  means  of  an  hydraulic  pump.  The  mercury 
which  is  displaced  by  the  water  passes  into  the 
lower  end  of  the  tube  T.  As  the  pressure  in- 
creases, the  mercury  gradually  rises,  and  com- 
presses the  gas  into  a  very  small  space  near  the 
top  of  the  tube. 

With  this  apparatus,  Cailletet1  subjected  oxygen 
and  carbon  monoxide  to  a  pressure  of  300  atmos- 
pheres and  a  temperature  of  —  29°.  The  tem- 
perature was  reduced  in  these  experiments  by 
means  of  liquid  sulphurous  acid.  When  the  heat, 
due  to  the  compression,  had  been  removed  from 
the  gas,  and  the  temperature  had  become  con- 
stant, the  pressure  was  suddenly  released.  In  both 
instances  a  mist  was  formed,  showing  that  a  par- 
tial condensation  had  taken  place.  These  observa- 
tions are  really  the  first  experimental  evidence  of 
the  liquefaction  of  the  so-called  permanent  gases. 
The  condensation  of  oxygen  by  Pictet  was  accom- 
plished about  three  weeks  later.  Cailletet's  work, 
however,  was  not  known  to  the  latter  experimenter 
at  that  time.  The  methods  employed  by  the  two 
investigators  were  entirely  different ;  and  both 
series  of  observations  may  be  considered  as  pio- 
neer experiments. 

1  Compt.  rend.,  85,  p.  1213. 


EXPERIMENTS   OF  CAILLETET  119 

Liquefaction  of  Nitrogen 

After  condensing  carbon  monoxide  and  oxygen 
to  the  liquid  state,  Cailletet  extended  his  researches 
to  other  gases  which  had  not  yet  been  liquefied. 
Pure  dry  nitrogen,1  when  subjected  to  a  pressure 
of  200  atmospheres  and  a  temperature  of  1 3°,  and 
then  suddenly  released,  formed  drops  of  liquid,  of 
an  appreciable  volume,  which  remained  in  the  tube 
for  a  period  of  three  seconds.  The  first  experiment 
was  made  at  a  temperature  of  —  29°.  The  author 
says  there  can  be  no  doubt  that  the  nitrogen  was 
actually  liquefied  in  these  experiments. 

Liquefaction  of  Air 

After  liquefying  the  gases  which  compose  the 
atmosphere,  Cailletet  proceeded  to  condense  ordi- 
nary air2  to  the  liquid  state.  He  says,  "Having 
liquefied  nitrogen  and  oxygen,  the  liquefaction  of 
air  follows  as  a  matter  of  course  ;  but  I  thought  it 
would  be  interesting  to  make  a  direct  experiment, 
which,  of  course,  succeeded  perfectly." 

Experiments  with  Hydrogen 

Cailletet  also  extended  his  experiments  to  hydro- 
gen.3 To  obtain  evidence  of  liquefaction  with  this 

1  Compt.  rend.,  85,  p.  1270.   2  Ibid.,  p.  1271.   3  Ibid.,  p.  1270. 


120  LIQUEFACTION   OF   GASES 

gas  was  a  matter  of  considerable  difficulty.  In 
the  first  experiment  no  peculiarities  were  observed. 
The  observation  was  repeated  many  times.  When 
the  gas  was  subjected  to  a  pressure  of  280  atmos- 
pheres, and  then  suddenly  released,  an  exceedingly 
fine  and  subtle  mist  was  formed  throughout  the 
length  of  the  tube.  The  duration  of  the  phenome- 
non was  extremely  short.  The  experiment  was 
successfully  repeated  a  number  of  times  in  the 
presence  of  Berthelot,  Deville,  and  Mascart. 

EXPERIMENTS  OF  PiCTET1 

Pictet's  work  on  the  liquefaction  of  oxygen  fur- 
nishes one  of  the  most  brilliant  experiments  of 
modern  science.  It  was  the  culmination  of  a  long 
experience  in  the  liquefaction  of  gases  and  the 
production  of  low  temperatures.  The  many  diffi- 
culties which  accompany  experiments  of  this 
nature  were  foreseen  and  provided  for.  In  the 
introduction  to  the  memoir  on  these  observations, 
we  find  that,  previous  to  the  experimental  part, 
Pictet  made  a  careful  study  of  the  problem.  He 
looked  upon  cohesion  as  a  property  common  to  the 
molecules  of  all  forms  of  matter ;  hence,  he  says, 
all  forms  of  matter  can  exist  in  the  gaseous,  liquid, 
or  solid  state.  He  recognized  clearly  that  press- 

1  Ann.  de  Chim.  et  de  Phys.  [5],  13,  p.  145;  Archives  des 
Sciences  Physiques  et  Naturelles,  1878,  p.  1 6. 


EXPERIMENTS   OF   PICTET  121 

ure  alone  would  not  suffice  for  the  condensation 
of  the  so-called  permanent  gases,  but  he  thought 
that  if  the  temperature  could  be  sufficiently  re- 
duced, the  molecular  cohesion  of  these  gases  would 
condense  them  into  liquids  or  solids. 

The  following  five  conditions  were  considered 
by  Pictet  to  be  essential  in  an  experiment  of  this 
nature : — 

1.  The  gas  to  be  liquefied  must  be  as  pure  as 
possible. 

2.  The  experimenter  must   be    able    to  obtain 
considerable  pressure,  and  also  be  able  to  measure 
this  pressure  accurately. 

3.  The  method  must  be  such  as  to  enable  the 
operator  not  only  to  obtain  a  very  low  temperature, 
but  to  maintain  this  temperature  indefinitely. 

4.  The  condensing  surface  exposed  to  the  low 
temperature  should  be  as  large  as  possible. 

5.  Provision    should    be  made   for   the    sudden 
expansion  of  the  gas  which  has  been  subjected  to 
this  low  temperature  and  high  pressure. 

These  conditions  were  all  fulfilled  in  the  care- 
fully constructed  apparatus  of  Pictet.  It  is  neces- 
sary, in  these  experiments,  that  the  heat  be 
removed  from  the  gas  as  rapidly  as  possible,  hence 
metallic  tubes  were  employed'instead  of  glass. 

The  apparatus  provides  for  three  distinct  opera- 
tions :  — 


122 


LIQUEFACTION   OF   GASES 


1.  The  circulation  of 
sulphurous  acid,  which 
produces  the  first  low- 
ering of  temperature. 

2.  The  circulation  of 
carbonic    acid    or    pro- 
toxide of  nitrogen,  which 
produces  a  second  low- 
ering  of    the   tempera- 
ture. 

3.  The  generation  of 
oxygen     in     a     closed 
vessel  provided  with  a 
long,  narrow  tube  which 
is    completely    sur- 
rounded by  the  carbonic 
acid. 

Figure  24  represents 
an  elevation  of  this  ar- 
rangement. U  and  V 
are  longitudinal  sec- 
tions of  two  large  drums. 
The  former  is  provided 
with  a  large  copper  tube 
R,  which  is  about  12  cm. 
in  diameter,  and  i.iom. 
in  length.  The  tube 
and  drum  are  slightly 


EXPERIMENTS   OF   PICTET  123 

inclined,  one  end  being  12  cm.  higher  than  the 
other. 

The  liquid  sulphurous  acid  is  introduced  into 
this  tube  through  the  pipe  s,  which  enters  at  the 
lower  end,  and  on  the  upper  side  of  the  tube.  At 
the  upper  end  of  the  tube  R  is  a  stop-cock  r  which 
is  connected  by  means  of  a  long  tube,  25  mm.  in 
diameter,  with  the  suction  of  the  first  pump  P. 

When  the  pump  is  operated,  and  a  partial 
vacuum  is  produced  in  the  tube  R,  the  sulphur- 
ous acid  will  begin  to  evaporate  immediately,  and 
the  temperature  of  the  liquid  will  fall  rapidly. 
The  more  perfect  the  vacuum,  the  lower  will  the 
temperature  fall. 

In  order  to  make  the  process  continuous  for  a 
period  of  several  hours,  it  was  necessary  to  make 
use  of  a  second  pump,  P'  (Fig.  25),  and  arrange 
the  two  so  that  the  suction  of  P'  corresponded  to 
the  pressure  of  P.  Experiment  showed  that,  by 
means  of  this  arrangement,  the  temperature  could 
be  reduced  almost  20°  farther  than  with  one  pump 
alone.  The  pumps  were  made  of  cast  iron.  The 
pistons  were  hollow,  and  provided  with  a  circula- 
tion of  water.  The  valves  were  carefully  con- 
structed of  steel.  The  speed  of  the  pumps  varied 
from  80  to  100  strokes  per  minute.  The  pistons 
of  the  two  pumps  were  connected  by  means  of  a 
metallic  pipe.  P'  was  connected  with  the  copper 


124  LIQUEFACTION   OF  GASES 


EXPERIMENTS    OF   PICTET  125 

condenser  C,  the  tubes  of  which  were  traversed  by 
a  current  of  water.  The  condenser  C  is  also  con- 
nected with  the  tube  z. 

The  action  is  as  follows :  The  sulphurous  acid 
which  is  evaporated  in  the  tube  R  passes  through 
the  cock  r  into  the  first  pump  P,  thence  into  the 
second  pump  P',  and  finally  into  the  condenser  C, 
where  it  is  compressed  to  from  i  to  2  atmospheres 
and  condensed  to  the  liquid  state.  From  the  con- 
denser C,  the  sulphurous  acid  passes  through  the 
pipe  s,  and  again  enters  the  tube  R.  The  quantity 
of  acid  which  passes  from  c  to  R  can  be  regulated 
by  means  of  the  screw-valve  q,  so  as  to  exactly 
replace  the  vapor  which  is  exhausted.  The  quan- 
tity of  liquid  then  in  the  tube  R  will  remain  con- 
stant. 

With  this  arrangement,  the  cycle  of  sulphurous 
acid  is  complete ;  and  the  fall  of  temperature 
produced  in  the  large  tube  R  can  be  perma- 
nently maintained. 

The  first  circulation  of  sulphurous  acid  is  only 
an  expedient  to  obtain  a  sufficient  quantity  of  car- 
bonic acid  or  protoxide  of  nitrogen  in  the  liquid 
state.  To  accomplish  this  a  tube  5,  6  cm.  in 
diameter  and  1.15  m.  in  length,  is  placed  in  the 
tube  R.  The  tube  S,  of  course,  is  completely 
immersed  in  the  liquid  sulphurous  acid,  and  has 
a  temperature  of  —65°.  At  this  temperature,  it 


126  LIQUEFACTION   OF   GASES 

requires  a  pressure  of  only  4  to  6  atmospheres  to 
condense  the  carbonic  acid. 

The  carbonic  acid  was  prepared  from  Carrara 
marble  and  hydrochloric  acid ;  it  was  then  care- 
fully washed  and  dried,  and  finally  stored  in  the 
oil  gasometer  G  (Figs.  24  and  25).  This  vessel 
was  connected,  by  means  of  the  tube  c,  with  the 
three-way  cock  K  (Fig.  25).  The  gaseous  car- 
bonic acid  was  pumped  from  the  vessel  G,  by 
means  of  the  pumps  O  and  O1 ,  which  are  similar 
in  every  respect  to  P  and  Pf,  and  compressed  in 
the  tube  S,  where  it  immediately  condensed  to  the 
liquid  state. 

The  next  step  was  to  utilize  the  liquid  carbonic 
acid  in  lowering  the  temperature  of  oxygen  gas. 
This  was  accomplished  in  the  drum  V,  which  is 
similar  to  U.  The  two  concentric  copper  tubes, 
D  and  A,  were  placed  in  this  drum,  which  was 
slightly  inclined,  but  in  the  opposite  direction  from 
that  of  U.  The  tube  D  was  3.70  m.  in  length  and 
35  mm.  in  external  diameter,  while  A  was  4.16  m. 
in  length  and  15  mm.  in  external  diameter.  The 
arrangement  is  shown  in  the  figures.  The  tube 
D  is  connected  with  the  tube  S,  which  contains 
the  liquid  carbonic  acid,  by  means  of  the  pipe  t. 
The  flow  of  acid  from  5  to  D  is  regulated  by 
means  of  the  screw-valve/.  The  pipe  c"  connects 
the  upper  part  of  D  with  the  three-way  cock  K. 


EXPERIMENTS   OF   PICTET  127 

By  turning  the  cock  K,  the  suction  of  the  pump 
O  is  brought  into  connection  with  the  tube  D  by 
means  of  the  pipes  c1  and  c".  The  pump  O'  is 
connected  with  the  tube  5  by  means  of  the  pipe  s. 

With  this  arrangement  the  cycle  of  carbonic 
acid  is  complete,  just  as  in  the  case  of  sulphurous 
acid.  The  directions  in  which  the  acids  flow  at 
different  parts  of  the  apparatus  are  shown  by  the 
arrows.  By  means  of  this  double  circulation  a 
temperature  of  from  —120  to  —140°  could  be 
obtained. 

The  tube  A  is  bent  downward  at  one  end  and 
connected  with  the  large  wrought-iron  flask  B. 
This  vessel,  with  a  capacity  of  1659  cc.,  was 
forged  with  the  utmost  care,  so  as  to  insure 
homogeneity  throughout  the  metal.  The  walls 
of  the  flask  were  35  mm.  in  thickness.  The  ves- 
sel B  contains  a  definite  quantity  of  a  perfectly 
dry  mixture  of  potassium  chlorate  and  potassium 
chloride.  On  heating  the  flask,  by  means  of  the 
gas  burner  b,  oxygen  gas  is  generated.  In  this 
way  a  pressure  of  several  hundred  atmospheres 
can  easily  be  obtained.  The  oxygen,  of  course, 
is  compressed  in  the  tube  A  as  well  as  in  the 
flask  B. 

After  the  apparatus  had  once  been  set  up,  fifteen 
days  were  spent  in  preliminary  experiments,  in 
order  to  test  separately  the  different  parts  of  the 


128  LIQUEFACTION   OF   GASES 

apparatus,  and  to  determine  the  conditions  under 
which  the  best  results  could  be  obtained.  A 
thousand  precautions,  he  says,  are  necessary  to 
insure  the  success  of  the  experiment.  After  all 
the  conditions  and  details  had  been  carefully 
studied,  Pictet  began  on  the  morning  of  Decem- 
ber twenty-second  to  make  a  complete  experiment. 
The  complete  working  of  the  apparatus  can  be 
understood  from  the  following  details  which  were 
given  concerning  the  first  experiment :  — 

9.00  A.M.  —  The  sulphurous  acid  pumps  are 
started.  The  temperature  in  the  tube  R  falls 
rapidly. 

9.30.  —  The  temperature  is  —55°.  The  car- 
bonic acid  pumps  are  started.  The  gasometer 
descends.  The  pressure  of  the  carbonic  acid  is 
6  atmospheres.  During  the  working  of  the  pumps 
the  pressure  slowly  increases  to  8  atmospheres. 

9.50. — The  temperature  is  —49°,  the  pressure 
8.5  atmospheres. 

I  stop  the  admission  of  carbonic  acid  to  the 
pumps. 

10.20. — Temperature  —65°,  pressure  3.9  at- 
mospheres. 

A  slight  quantity  of  gas  is  again  admitted. 

10.40. — Temperature  —60°,  pressure  5  atmos- 
pheres. 


EXPERIMENTS    OF   PICTET  129 

800  litres  of  carbonic  acid  are  now  liquefied. 
Hoar-frost  covers  the  lower  part  of  the  manom- 
eter m' . 

10.50. — The  wrought-iron  flask  is  screwed  on 
to  the  tube  A.  It  is  charged  with  a  mixture  of 
700  grams  of  potassium  chlorate  and  250  grams 
of  potassium  chloride  powdered  together  in  a 
mortar,  sifted  and  carefully  dried. 

i  i.oo.  —  The  gas  under  the  flask  is  lighted. 

Carbonic  acid  is  admitted  more  freely  into  the 
pumps.  The  pressure  increases  to  10  atmos- 
pheres ;  the  temperature  is  —  48°.  The  appear- 
ance of  frost  on  the  pipe  c"  indicates  that  the 
carbonic  acid  has  passed  over  into  the  long 
tube  D. 

11.15.  —  The  pipe  c"  is  connected  with  the  suc- 
tion of  the  pumps.     The  temperature  of  the  car- 
bonic acid  reaches  a  minimum,  —  130°. 

11.35.  —  The  manometer  m1  on  the  oxygen  tube 
records  a  pressure  of  5  atmospheres. 

The  circulation  of  sulphurous  and  carbonic  acids 
is  completely  established. 

12. 10  P.M.  —  The  oxygen  manometer  records  a 
pressure  of  50  atmospheres. 

12. 16.  —  The   pressure    increases   to   60  atmos- 
pheres, and  then  gradually  rises  as  follows  :  — 


130  LIQUEFACTION   OF   GASES 

12.23  pressure,     70  atmospheres. 

12.29  "  8o 

12.34  "  9°  " 

12.36  "         100 

12.37  "         150  " 

12.37.25"  "  200  " 

12.38  "       460 

12.39  "  510  " 
12.39.30"        "  522 

12.40  "  525 
12.42  "  526 
12.44  "  525 
12.48  "  505 
12.50  "  495 

i. oo  "        471 

1.05.  —  The  pressure  is  471  atmospheres. 

The  pressure  is  stationary ;  hence  all  the  chem- 
ical and  physical  phenomena  have  terminated. 

The  condensation  has  produced  the  fall  of  press- 
ure recorded  by  the  manometer.  The  tube  A  is 
filled  with  liquid  oxygen. 

There  is  evidently  an  excess  of  gas,  which  causes 
a  higher  pressure  than  that  corresponding  to  the 
temperature  of  the  liquid  carbonic  acid. 

1. 10.  —  The  pressure  is  exactly  470  atmospheres. 
The  plug  which  closes  the  tube  A  is  opened. 
A    liquid    jet   issues   with    great   violence,  and 


EXPERIMENTS   OF   PICTET  131 

assumes  the  appearance  of  a  brilliant  white  pencil. 
A  bluish  halo  surrounds  the  jet,  especially  the 
lower  part.  The  jet  of  liquid  is  from  10  to  12 
cm.  in  length,  and  about  1.5  to  2  cm.  in  diameter. 
It  continues  for  a  period  of  3  or  4  seconds. 

The  regulating  cock  is  closed.  The  pressure  is 
396  atmospheres,  but  falls  rapidly  to  352  atmos- 
pheres, where  it  remains  stationary  for  about  3 
minutes. 

1. 18. — The  tube  is  again  opened;  a  second 
liquid  jet,  similar  to  first,  issues.  But  following 
this,  the  gas  escapes  with  a  characteristic  aeriform 
appearance. 

The  gas,  in  expanding,  produces  a  mist  by  par- 
tial condensation.  The  appearance,  however,  is 
quite  different  from  that  of  the  first  jet.  This 
indicates  an  absence  of  liquid  in  the  tube. 

1.19. — The  pressure  is  50  atmospheres.  The 
gas  escapes  as  a  bluish  mist,  but  there  is  no  evi- 
dence of  liquid  being  carried  with  it. 

Live  coals,  when  placed  under  the  second  jet, 
blaze  up  instantly  with  great  violence. 

This  experiment  demonstrated  clearly  that  oxy- 
gen can  be  condensed  to  the  liquid  state.  Pictet 
calls  special  attention  to  the  difference  between 
the  mist  produced  by  the  expansion  of  the  gas 
alone,  and  that  produced  when  there  was  liquid  in 
the  tube.  The  change,  he  says,  from  one  to  the 


132  LIQUEFACTION   OF   GASES 

other  was  so  apparent  that  it  was  noticed  by  more 
than  twenty  spectators  at  the  same  moment. 

Five  experiments  were  made,  three  with  car- 
bonic acid,  and  two  with  protoxide  of  nitrogen. 
The  same  quantity  of  potassium  chlorate  and 
potassium  chloride  was  used  in  each  of  these 
experiments. 

The  more  important  observations  refer  to  five 
successive  stages,  which  the  author  designates  as 
follows :  — 

1 .  The  maximum  stationary  pressure  of  the  oxy- 
gen before  the  first  jet  is  allowed  to  escape. 

This  pressure  is  always  stationary  for  at  least 
a  quarter  of  an  hour,  and  is  always  less  than  the 
pressure  recorded  at  the  end  of  the  chemical 
reaction. 

2.  The  pressure    immediately   after  the   escape 
of  the  first  jet,  when  it  is  distinctly  observed  that 
the  liquid  has  been  replaced  by  a  gaseous  jet. 

3.  The  stationary  pressure  after  the  first  jet. 
The  fall  of  pressure  in  this  operation  is  due  to 

the  condensation  of  oxygen. 

When  the  tube  is  filled  a  second  time,  condensa- 
tion ceases,  and  the  pressure  becomes  stationary. 

4.  The  pressure  immediately  after  the  second  jet. 

5.  The  stationary  pressure  after  the  second  jet. 
The  third  jet  was  never  complete  ;  it  was  always 


EXPERIMENTS   OF   PICTET 


133 


shorter  than  the  first  two.  This  indicated  that  the 
condensation  was  not  sufficient  to  fill  the  tube 
three  times. 

These  pressures  for  five  different  experiments 
on  the  liquefaction  of  oxygen  are  shown  in  the 
following  table.  The  pressures  are  given  in  atmos- 
pheres :  — 


NUMBER  OF  EXPERIMENT 

i 

2 

3 

4 

5 

I.    Maximum   stationary  pressure 
before  the  first  jet  . 
2.    Pressure  immediately  after  the 
first  jet                          ... 

470 
367 
308 
285 
274 

0 

471 

395 
339 
290 

271 
245 
253 

0 

471 
432 
378 
29I 
272 

o 

469 
4OO 
346 
285 
25I 
215 

218 

0 

469 
4l6 
361 
296 

253 
205 
212 

0 

3.    Stationary  pressure  after   the 
first  jet 

4.    Pressure  immediately  after  the 
second  iet 

5.    Stationary  pressure   after   the 
second  jet     

6.    Pressure  immediately  after  the 
third  jet    

7.    Stationary   pressure    after    the 
third  jet                   .... 

8.    Pressure  after  the   fourth  jet. 
In  this  case  the  jet  was  en- 
tirely °"aseous     

Pictet  endeavored  to  determine  the   density  of 
liquid    oxygen.       The    method,    of     course,    was 


134  LIQUEFACTION   OF   GASES 

indirect,  and  involved  numerous  calculations.  In 
the  original  memoir,  several  pages  are  devoted  to 
this  part  of  the  experiment.  He  concluded  that 
the  density  of  liquid  oxygen  was  very  nearly 
equal  to  that  of  water.  Later  researches  have 
shown  the  density  to  be  slightly  greater  than 
that  of  water,  but  considering  the  data  upon 
which  Pictet  based  his  calculations,  the  result  is 
remarkably  accurate. 

Measurements  on  the  vapor-pressure  of  liquid 
oxygen  showed  it  to  be  about  270  atmospheres  at 
the  temperature  of  the  liquid  carbonic  acid,  and 
about  250  atmospheres  at  the  temperature  obtained 
by  means  of  the  protoxide  of  nitrogen. 

Solidification  of  Oxygen 

In  the  third  and  fourth  experiments  the  escap- 
ing jet  was  carefully  examined  by  means  of  an 
electric  light.  The  jet  appeared  to  consist  of  two 
parts ;  a  central  portion  of  2  to  3  mm.  in  diameter, 
and  an  outer  envelope.  It  resembled  two  con- 
centric cylinders,  the  inner  of  which  was  partially 
transparent,  while  the  outer  appeared  as  snow- 
white  dust.  The  light  reflected,  by  the  dust,  at 
right  angles  to  the  incident  ray  was  examined 
by  means  of  a  polariscope,  and  found  to  be  parti- 
ally polarized.  This  examination  was  made  by 


EXPERIMENTS   OF   PICTET  135 

M.  H.  Dufour,  Professor  of  Physics  in  the  Acad- 
emy of  Lausanne.  Although  the  experiment  was 
not  conclusive  evidence,  it  was  thought  by  those 
present  that  the  outer  portion  of  the  jet  consisted 
of  solid  particles  of  oxygen. 

Experiments  with  Hydrogen 

"  Having  obtained  the  preceding  results  with 
oxygen,"  Pictet  says,  "we  were  naturally  induced 
to  treat  hydrogen  in  a  similar  manner.  The  entire 
mechanical  apparatus  used  for  the  first  gas  can  be 
used  for  the  second  without  alteration." 

In  this  experiment  the  hydrogen  was  generated 
from  1261  grams  of  potassium  formate  and  500 
grams  of  caustic  potash.  The  two  were  mixed 
together,  and  carefully  dried. 

The  temperature  was  lowered  by  means  of 
sulphurous  acid  and  protoxide  of  nitrogen.  The 
method  of  procedure  was  exactly  the  same  as  in 
the  case  of  oxygen. 

The  following  are  some  of  the  notes  recorded  in 
the  first  experiment,  which  was  begun  at  7  P.M. 
Jan.  10,  1878  :  — 

The  pumps  were  started  at  7  o'clock,  and 
when  the  circulation  of  the  two  acids  was  com- 
plete, the  gas  under  the  hydrogen  generator  was 
lighted. 


136  LIQUEFACTION  OF   GASES 

8.32      P.M.  —  The  pressure  of  hydrogen  was    50  atmospheres. 

8.47                      "                   "  "         100  " 

9.00                      "                   "  "        200  " 

9.04                      "                   "  "        300  « 

9.06.  i  $"              "                  "  "        400  « 

9.07  '       "       «  "   500  « 

9.08  «       «  «    550  « 
9.10.30"      "       "  "    640  " 
9.11         «       "  «    650  « 
9.11.30"      "       "  «    652  " 


At  this  point  the  pressure  became  almost  sta- 
tionary, and  the  tube  containing  the  hydrogen  was 
opened.  An  opaque  jet  of  a  bluish  tint  issued 
from  the  orifice.  The  jet  became  intermittent, 
and  Pictet  concluded  that  the  hydrogen  had  solidi- 
fied at  the  opening  in  the  tube. 

From  the  observations  recorded  in  this  experi- 
ment, there  can  be  but  little  doubt  that,  at  the 
moment  when  the  pressure  was  relieved,  the 
hydrogen  was  partially  liquefied  and  probably 
solidified. 

Cailletet  and  Pictet  removed  the  last  doubt  as  to 
the  possibility  of  liquefying  such  gases  as  oxygen, 
nitrogen,  and  hydrogen.  The  idea  of  permanent 
gases  is  no  longer  tenable.  Since  these  experi- 
ments were  made,  the  apparatus  for  the  liquefac- 
tion of  gases  has  been  materially  modified  and 
improved.  The  names  of  these  two  investigators, 
while  connected  especially  with  the  pioneer  work 


EXPS.    OF   WROBLEWSKI   AND    OLSZEWSKI     137 

in  the  liquefaction  of  the  permanent  gases,  are 
associated  also  with  the  names  of  the  more  recent 
experimenters. 

LIQUEFACTION  OF  OZONE  BY  HAUTEFEUILLE  AND 
CHAPPUIS 

In  1882  Hautefeuille  and  Chappuis  condensed 
ozone  to  the  liquid  state.1  The  gas  was  com- 
pressed in  the  Cailletet  apparatus  to  a  pressure  of 
125  atmospheres.  The  temperature  was  lowered 
by  means  of  a  jet  of  liquid  ethylene  to  about 
—  100°.  Under  these  conditions  the  gas  con- 
densed to  an  indigo-blue  liquid.  The  liquid  re- 
mained for  a  short  time  in  a  static  condition  at 
the  ordinary  atmospheric  pressure.  The  authors 
state  that  the  ozone  probably  contained  some  oxy- 
gen. This  gas  has  been  liquefied  by  later  expe- 
rimenters, who  have  also  determined  its  critical 
constants  and  boiling  point. 


SECTION  II 
EXPERIMENTS  OF  WROBLEWSKI  AND  OLSZEWSKI 

In    1883  the  names  of  two  brilliant  scientists, 
Wroblewski  and  Olszewski,  were  added  to  the  list 

1  Compt.  rend.,  94,  p.  1249. 


138  LIQUEFACTION   OF   GASES 

of  experimenters  on  the  liquefaction  of  gases. 
These  two  observers,  co-workers  at  times,  and 
independent  investigators  at  other  times,  have 
done  much  to  bring  about  the  present  state  of 
perfection  in  the  methods  employed  in  the  con- 
densation of  gases. 

Their  first  work  in  this  direction  consisted  in 
the  liquefaction  of  oxygen,  nitrogen,  and  carbon 
monoxide.1  Acting  upon  the  suggestion  of  Caille- 
tet  they  employed  liquid  ethylene  as  a  refrigerant. 

The  apparatus  employed  is  represented  in  fig- 
ures 26  and  27.  The  gas  was  compressed  by 
means  of  the  contrivance2  shown  in  figure  26. 
The  gas  is  introduced  into  the  large  glass  tube  i 
which  rests  in  the  hollow  iron  cylinder  a  b.  The 
upper  end  of  the  cylinder  is  closed  air-tight  by 
means  of  the  brass  contrivance  d%  which  is  held  in 
its  position  by  means  of  the  brass  screw  c.  A 
small  steel  tube  extends  from  the  upper  end  of 
the  tube  i  throughout  the  brass  portion  d.  The 
side  tube  /  serves  to  connect  the  interior  of  the 
apparatus  with  a  manometer  and  a  Cailletet  pump. 
The  method  of  operation  is  similar  to  that  of 
Cailletet.  The  large  tube  i  and  the  smaller  tube 

1  Wied.  Ann.,  20,  p.  243,  1883. 

2  This  portion  of  the  apparatus  was  constructed  by  Wroblewski 
in    1882,  for   the    purpose   of  studying   surface   tension.     Compt. 
rend.,  95,  pp.  284  and  342. 


EXPS.   OF  WROBLEWSKI  AND   OLSZEWSKI     139 


FIG.  26. 


140 


LIQUEFACTION   OF   GASES 


above  are  filled  with  the  gas  to  be  compressed. 
Mercury  is  then  introduced  through  /  until  the  de- 
sired pressure  is  obtained.  The  resisting  strength 
of  the  apparatus  was  estimated  to  be  about  500 
atmospheres. 


FIG.  27. 


EXPS.    OF   WROBLEWSKI    AND    OLSZEWSKI     141 

The  liquefying  apparatus  is  represented  in  fig- 
ure 27.  The  compression  apparatus  is  shown  in 
the  lower  right-hand  corner.  In  this  case,  how- 
ever, the  steel  tube  d  is  replaced  by  the  thick- 
walled  capillary  glass  tube  q  which  is  fused  into 
the  upper  end  of  the  tube  i.  The  tube  i,  together 
with  the  small  tube  q,  has  a  capacity  of  about  200 
cubic  centimetres.  These  tubes  are  filled  with  the 
gas  to  be  liquefied  by  means  of  a  Jolly  mercury 
pump.  The  tube  q  passes  air-tight  into  the  glass 
vessel  s  which,  in  turn,  is  closed  air-tight  by  means 
of  a  rubber  stopper,  t  is  a  hydrogen  thermometer 
constructed  on  the  principle  of  the  Jolly  air  ther- 
mometer. The  copper  tube  w,  which  passes 
through  the  T^tube  //,  leads  to  the  liquid  ethylene 
in  the  receiver  x  of  a  Natterer  compression  pump. 
This  receiver  rests  in  the  large  zinc  vessel  s  which 
contains  a  freezing  mixture.  The  spiral  portion 
of  the  tube  w  is  surrounded  by  solid  carbonic  acid 
and  ether  in  the  vessel  b.  The  side  tube  of  u  is 
connected  with  the  lead  tube  i>,  which  leads  to  a 
Bianchi  exhaust  pump.  The  liquid  ethylene  then 
can  be  evaporated  under  reduced  pressure. 

Liquefaction  of  Oxygen 

The  oxygen  gas  was  prepared  from  pure  potas- 
sium perchlorate,  washed  with  caustic  potash,  and 
dried  by  means  of  concentrated  sulphuric  acid. 


142  LIQUEFACTION   OF   GASES 

The  tubes  i  and  q  were  then  filled  with  the  gas. 
The  tube  q  was  cooled  down  to  a  temperature  of 
—  130°.  The  pressure  was  then  increased  to  more 
than  twenty  atmospheres,  when  the  gas  was  com- 
pletely liquefied.  The  liquid  oxygen  collected  in 
the  lower  end  of  tube  q,  and  showed  a  well-defined 
meniscus.  Measurements  were  made  of  the  vapor- 
pressure  at  different  temperatures. 

Liquefaction  of  Nitrogen  and  Carbon  Monoxide 

After  the  successful  experiment  on  the  liquefac- 
tion of  oxygen,  the  investigation  was  extended  to 
nitrogen  and  carbon  monoxide.  When  subjected 
to  a  temperature  of  —  136°,  and  a  pressure  of  150 
atmospheres,  both  of  these  substances  remained  in 
the  gaseous  condition.  When  the  pressure  was 
suddenly  released,  however,  there  was  evidence  of 
liquefaction  in  the  tube.  By  relieving  the  press- 
ure more  slowly  and  keeping  it  always  above  50 
atmospheres,  the  nitrogen  and  carbon  monoxide 
were  both  obtained  as  liquids  in  a  static  condition. 
The  liquids  were  transparent  and  colorless,  and 
showed,  in  each  case,  a  well-defined  meniscus. 

These  observations  were  the  beginning  of  a  long 
series  of  experiments  by  these  investigators.  Their 
later  researches  were  carried  on  independently, 
and  will  be  considered  presently. 


EXPERIMENTS   OF  WROBLEWSKI  143 

DEMONSTRATION  OF  THE  LIQUEFACTION  OF 
OXYGEN  BY  DEWAR 

During  the  next  year  after  the  liquefaction  of 
oxygen  and  nitrogen  by  Wroblewski  and  Ols- 
zewski,  James  Dewar  of  London  described  an 
apparatus1  for  demonstrating  the  liquefaction  of 
oxygen  in  the  lecture  room.  Since  that  time  he 
has  been  a  constant  worker  in  the  field  of  the 
liquefaction  of  gases,  and  is  the  author  of  many 
important  contributions. 

From  this  point  it  is  probably  advisable  to  con- 
sider the  work  of  Wroblewski,  Olszewski,  and 
Dewar  separately.  The  historical  development  of 
the  methods  can  be  gathered  from  the  dates  of  the 
experiments. 

EXPERIMENTS  OF  WROBLEWSKI 

Soon  after  the  experiments  of  Wroblewski  and 
Olszewski  on  the  liquefaction  of  oxygen,  air,  nitro- 
gen, etc.,  in  1883,  the  former  experimenter  made 
some  important  observations  in  the  same  field. 
Early  the  next  year  he  subjected  hydrogen  2  to  a 
pressure  of  100  atmospheres  in  a  small  glass  tube. 
The  temperature  of  the  gas  was  lowered  by  the 
evaporation  of  liquid  oxygen  which  surrounded  the 

1  Proc.  Roy.  Inst.,  1 1,  p.  148;   Phil.  Mag.,  18,  p.  210,  1884. 

2  Compt.  rend.,  98,  p.  149,  1884. 


144 


LIQUEFACTION   OF   GASES 


liquefying  tube.  On  suddenly  releasing  the  press- 
ure, signs  of  ebullition  were  observed  in  the  tube, 
showing  that  the  hydrogen  had  been  partially 
liquefied. 

In  April  of  the  same  year  Wroblewski  published 
an  article l  on  the  boiling  points  of  oxygen,  air, 
nitrogen,  and  carbon  monoxide.  The  boiling  points 
of  oxygen  under  different  pressures  were  as 
follows :  — 


Pressure 


Boiling  Point 


50      atmospheres 
27.02  " 

24.40  « 

22.20  " 


—   II30 

-  129.6 

-  1334 

-  135-8 

-  184. 


The  last  temperature  represents  the  boiling 
point  of  oxygen  under  the  ordinary  atmospheric 
pressure.  The  following  values  were  obtained  for 
the  boiling  points  of  air,  carbon  monoxide,  and 
nitrogen  under  a  pressure  of  one  atmosphere :  — 


Substance 

Boiling  Point 

Carbon  monoxide 
Air 
Nitrogen 

-  1  86° 
-  192.2 
-  194-3 

1  Compt.  rend.,  98,  p.  982,  1884. 


EXPERIMENTS   OF   WROBLEWSKI  145 

By  evaporating  liquid  air  and  nitrogen  under 
reduced  pressure,  a  temperature  of  —  200°  was 
obtained.  The  author  stated  in  this  article  that 
atmospheric  air  will  be  the  refrigerant  of  the 
future. 

A  few  months  later  the  same  experimenter1 
liquefied  methane  and  studied  its  properties.  The 
critical  temperature  he  found  to  be  —  73°. 5,  and 
the  critical  pressure  56.8  atmospheres.  The  boil- 
ing point,  he  says,  is  between  —  155°  and  —  160°. 
By  using  liquid  marsh-gas  as  a  refrigerant,2  the 
author  states  that  oxygen,  air,  carbon  monoxide, 
and  nitrogen,  may  be  liquefied  at  comparatively 
low  pressures. 

In  1885  Wroblewski  published  a  detailed  ac- 
count of  the  apparatus3  employed  by  him  in  the 
liquefaction  of  oxygen,  carbon  monoxide,  air,  nitro- 
gen, etc.  The  plan  of  the  apparatus  is  shown  in 
figure  28. 

The  two  iron  cylinders,  a  and  b,  previously 
tested  to  150  atmospheres  pressure,  are  provided 
at  the  ends  with  the  screw-cocks  c,  d,  e,  and  /. 
The  two  vessels  are  connected  with  each  other 
and  with  the  manometer  h  by  means  of  the  cop- 

1  Compt.  rend.,  99,  p.  136,  1884. 

2  The  use  of  liquid  methane  as  a  refrigerant  was  first  suggested 
by  Dewar,  Nature,  28,  p.  551,  1883. 

3  Wien.  Ber.,  91,  p.  672,  1885;   Wied.  Ann.  25,  p.  371,  1885. 

L 


146 


LIQUEFACTION   OF   GASES 


per  tube  gg.  This  connection,  however,  can  be 
interrupted  at  any  time  by  means  of  the  screw- 
cocks  at  the  ends  of  the  vessels.  The  cylinders 
are  fastened  by  means  of  the  metal  strip  i  in  the 


FIG.  28. 


zinc  chamber  k,  which  can  be  filled,  if  desirable, 
with  a  freezing  mixture.  The  copper  tube  /,  about 
three  metres  in  length,  is  connected  with  a  Natterer 
pump.  The  screw-cock  e  is  connected  by  means 
of  the  tube  m  with  the  steel  contrivance  ;/,  which 


EXPERIMENTS   OF  WROBLEWSKI  147 

in  turn  is  connected  with  the  liquefying  apparatus 
and  the  air  manometer  o.  This  contrivance  is  held 
firmly  in  its  position  by  means  of  the  iron  frame  q. 
The  pressure  in  the  vessel  a  is  increased  to  the 
liquefying  pressure,  not  less  than  40  atmospheres, 
while  in  b  it  ranges  from  100  to  120  atmospheres. 
Each  of  the  vessels,  a  and  b,  contain  small  cylin- 
ders of  calcium  chloride  and  caustic  potash,  to 
remove  any  moisture  and  carbon  dioxide  from  the 
gas. 

The  gas  is  liquefied  in  the  thick-walled  glass 
tube  r,  42  to  46  cm.  in  length,  which  is  capable  of 
resisting  a  pressure  of  60  atmospheres.  The  lower 
end  of  the  tube  is  sealed,  while  the  upper  end  is 
cemented  into  the  brass  flange  s,  and  is  closed  air- 
tight by  means  of  the  contrivance  /.  The  opening 
v  is  connected  by  means  of  the  copper  tube  w  with 
n,  which  in  turn  is  connected  with  the  compression 
cylinders.  The  opening  x  serves  for  the  introduc- 
tion of  a  thermometer  which,  in  this  case,  was  a 
thermo-electric  pair  connected  with  a  sensitive  re- 
flecting galvanometer.  The  tube  x  is  placed  in  a 
larger  tube  mf,  which  is  connected  with  the  cylin- 
.der  d'  containing  liquid  ethylene.  The  tube  mf, 
in  turn,  rests  in  the  larger  tube  yt  and  communi- 
cates with  it  at  the  small  opening  n'.  The  vessel 
r'  contains  solid  carbonic  acid  and  ether,  through 
which  the  liquid  ethylene  must  pass  before  it 


148  LIQUEFACTION   OF   GASES 

reaches  the  liquefying  tube.     The  ethylene  vapors 
pass   out   of   the   apparatus  through  the  tube  f, 
which  is  connected  with  an  air-pump  to  reduce  the 
pressure.     At  a  pressure  of  about  10  mm.  of  mer- 
cury the  temperature  sank  to  —  152°.     When  the 
temperature  is  thus  lowered,  the  pressure  in  the 
liquefying  tube  is  increased   to    about  40   atmos 
pheres,  when  the  gas  condenses  to  the  liquid  state 
Considerable  care  is  required  to  get  the  apparatus 
filled  with  perfectly  dry  gas. 

In  this  way  Wroblewski  liquefied  oxygen  in 
considerable  quantity,  and  kept  it  in  a  static  con- 
dition, at  the  ordinary  atmospheric  pressure,  for  a 
period  of  a  quarter  of  an  hour.  He  also  liquefied 
nitrogen,  air,  and  carbon  monoxide,  and  studied 
their  properties.  The  following  values  were  ob- 
tained by  him  for  the  critical  constants  of  these 
gases :  — 


Substance 

Critical 
Temperature 

Critical  Pressure 

Oxygen     
Carbon  monoxide  .     . 
Nitrosfen 

-118 
—  140.2 

I  AC    C 

50  atmospheres 
39 

1C                " 

1T-->O 

oy 

The  author  also  made  a  careful  study  of  the 
measurement  of  low  temperatures.  For  this  pur- 
pose he  made  use  of  a  copper-German-silver 


EXPERIMENTS   OF  WROBLEWSKI  149 

thermo-electric  pair  and  a  sensitive  reflecting  gal- 
vanometer. Previous  to  the  measurements,  the 
apparatus  was  compared  with  a  hydrogen  ther- 
mometer. By  the  evaporation  of  oxygen  at  dif- 
ferent pressures,  the  following  temperatures  were 
obtained :  — 


Pressure 

Temperature 

74  cm.  of  mercury 

-  i8i°.5 

1  6        «        « 

-  190.0 

10            "            " 

-  190.5 

8        "        " 

-  191.98 

6        "        " 

-  194-4 

4        «        « 

-  197-7 

2            u            " 

—  200.4 

The  oxygen  in  these  experiments  was  partially 
solidified. 

The  following  temperatures  were  obtained  by 
the  evaporation  of  carbon  monoxide :  — 

Pressure  (in  cm.  of  mercury)  : 

73.5         16  10  64 

Temperature : 

-190°     -197°.  5     -I98°.83     -2oi°.5     -2oi°.6 

The  carbon  monoxide  was  completely  solidified. 
The  temperatures  obtained  by  the  evaporation  of 
liquid  nitrogen  are  as  follows  :  — 

Pressures:  74  12  8  6  4.2 

Temperatures:    -193°      —201°      —201°. 7      —204°      —206° 


150  LIQUEFACTION   OF  GASES 

The  nitrogen  at  the  lowest  temperature  was 
partially  solidified. 

The  author  also  determined  the  vapor-pressures 
of  liquid  oxygen,  carbon  monoxide,  and  nitrogen  at 
different  temperatures. 

Liquefaction  of  Air 

In  1885  Wroblewski  made  an  elaborate  series  of 
experiments  on  the  liquefaction  of  air.1  The  ap- 
paratus employed  was  similar  to  that  represented 
in  figure  28.  The  object  of  these  experiments 
was  to  separate  liquid  air  into  two  distinct  layers. 

In  a  preliminary  experiment,  a  mixture  of  five 
parts  of  carbonic  acid  and  one  part  of  air,  at  a 
temperature  of  o°,  was  compressed  until  a  portion 
of  the  gas  was  condensed  to  the  liquid  state.  In 
this  condition  the  gas  and  liquid  in  the  tube  were 
separated  by  a  well-defined  meniscus.  As  the 
pressure  was  increased,  the  meniscus  became  less 
distinct,  and  finally  disappeared  at  the  instant 
when  the  optical  density  of  the  gas  became  equal 
to  that  of  the  liquid.  By  increasing  the  pressure 
still  further,  a  second  meniscus  was  produced, 
which  occupied  a  much  higher  position  than  the 
first.  In  this  condition  the  tube  contained  two 
liquids,  separated  by  a  sharp  meniscus.  After  a 

1  Wied.  Ann.,  26,  p.  134. 


EXPERIMENTS   OF  WROBLEWSKI  151 

time  the  liquids  mixed  completely,  and  formed  a 
homogeneous  liquid. 

In  a  similar  manner  liquid  atmospheric  air  was 
obtained  in  two  distinct  layers,  separated  by  a 
well-defined  meniscus.  The  air  was  partially  lique- 
fied at  a  temperature  of  — 142°,  which  is  above  the 
critical  temperature  of  nitrogen.  When  the  press- 
ure was  increased  to  40  atmospheres,  the  meniscus 
which  separated  the  liquid  from  the  gas  disap- 
peared. The  temperature  was  then  lowered,  and, 
at  a  pressure  of  37.8  atmospheres,  a  second  menis- 
cus was  formed,  which  occupied  a  higher  position 
than  the  first.  The  air  in  this  condition  consisted 
of  two  layers  of  liquid  separated  by  a  sharp  menis- 
cus. Analysis  showed  that  the  lower  layer  con- 
tained about  three  per  cent  more  oxygen  than 
the  upper  layer.  After  a  couple  of  minutes  the 
two  liquids  mixed  and  formed  a  homogeneous 
fluid. 

The  author  also  made  a  large  number  of  obser- 
vations on  the  vapor-pressure  of  liquid  air  at  dif- 
ferent temperatures.  He  also  studied  carefully 
the  changes  of  temperature  and  pressure  which 
accompanied  the  mixture  of  the  two  layers  of 
liquid  air. 

In  addition  to  the  experiments  which  have  been 
outlined,  Wroblewski  made  numerous  observations 
on  the  properties  of  matter  at  low  temperatures. 


152  LIQUEFACTION   OF  GASES 

He  also  made  a  study  of  the  relation  between  the 
gaseous  and  liquid  states  of  matter.1  At  the  early 
age  of  forty  years,  just  in  the  midst  of  his  active 
career,  he  met  with  a  fatal  accident.  "While 
working  late  at  night  in  his  laboratory,  he  fell 
asleep,  and  in  his  sleep  he  overthrew  a  kerosene 
lamp.  His  clothing  began  to  burn,  and  the  wounds 
thus  received  resulted,  four  days  later,  in  death." 
"The  value  of  Wroblewski's  supplement  to  the 
work  of  Cailletet  and  Pictet  cannot  be  easily 
estimated,  and  we  deplore  the  occurrence  of  the 
fatal  accident  which  robs  the  scientific  world  of 
such  an  able  experimenter  in  this  important 
department  of  chemistry."2 

EXPERIMENTS  OF  OLSZEWSKI 

During  the  first  few. years  of  investigation  in 
the  field  of  the  liquefaction  of  gases,  Olszewski's 
experiments  were  somewhat  similar  to  those  of 
Wroblewski.  The  work  of  these  two  observers 
was  carried  on  simultaneously  until  the  death  of 
the  latter  in  1888. 

Soon  after  the  liquefaction  of  oxygen,  nitrogen, 

1  Wied.  Ann.,  29,  p.  428,  1886. 

2  Wroblewski's  work  on  the  liquefaction  of  gases  has  been  pub- 
lished in  the  form  of  a  pamphlet  entitled,   Comment  Vair  a  ete 
Liquefie.  —  Ref.  Devvar,  Chem.  News,  73,  p.  42. 


EXPERIMENTS   OF   OLSZEWSKI  153 

etc.,  by  Wroblewski  and  Olszewski  in  1883,  the 
latter  experimenter  made  use  of  liquid  oxygen  as 
a  refrigerant  in  the  liquefaction  of  other  gases. 
In  1884  he  subjected  hydrogen  *  to  a  pressure  of 
nearly  200  atmospheres,  and  at  the  same  time 
cooled  the  gas  to  the  temperature  of  liquid  oxygen 
(boiling  under  a  pressure  of  6  mm.  of  mercury). 
Under  these  conditions,  hydrogen  showed  no 
meniscus,  but  when  the  pressure  was  suddenly  re- 
leased a  momentary  ebullition  was  observed.  The 
author  concluded  that,  at  the  temperature  obtained 
by  the  evaporation  of  liquid  oxygen  under  reduced 
pressure,  it  is  impossible  to  obtain  liquid  hydrogen 
in  a  static  condition. 

The  experiments  on  hydrogen  were  repeated 
during  the  same  year,  with  similar  results.2  In 
this  series  of  experiments  the  author  determined 
the  critical  pressure  of  nitrogen,  and  found  it  to  be 
39.2  atmospheres. 

Olszewski  also  made  a  large  series  of  experi- 
ments on  the  production  of  low  temperatures  by 
the  evaporation  of  liquid  oxygen,  nitrogen,  air,  etc. 
under  reduced  pressure.  The  apparatus3  employed 
by  him  in  the  earlier  experiments  on  the  liquefac- 
tion of  gases  is  represented  in  figure  29. 

The  gas  is  liquefied  in  the  thick-walled  glass  tube 

1  Compt.  rend.,  98,  p.  365.  2  Ibid.,  p.  913. 

3  Wied.  Ann.,  31,  p.  58. 


'54 


LIQUEFACTION   OF  GASES 


a,  which  is  30  centimetres  in  length,  and  14  milli- 
metres in  diameter.     The  lower  end  of  this  tube 


is  sealed  off,  while  the  upper  end  is  slightly  wi- 
dened, and  fastened  in  the  brass  flange   b,  which 


EXPERIMENTS   OF   OLSZEWSKI  155 

screws  into  the  brass  contrivance  c.  The  tube  d 
represents  a  hydrogen  thermometer.  The  liquefy- 
ing tube  a  is  connected,  by  means  of  the  copper 
tube  e,  ist,  with  the  manometer  f,  which  serves  for 
the  measurement  of  high  pressures  lower  than  I  at- 
mosphere ;  2d,  with  the  air  manometer  g  for  the 
measurement  of  high  pressures  ;  3d,  with  a  vacuum- 
pump;  4th,  with  the  aspirator  r\  5th,  with  the 
Natterer  receiver  /,  by  means  of  which  a  pressure 
of  60  to  80  atmospheres  may  be  obtained.  The 
tube  a  is  placed  in  a  system  of  concentric  glass 
tubes,  which  communicate  with  each  other  at  the 
top.  The  outer  tube  is  connected  with  an  exhaust- 
pump  by  means  of  the  pipe  n.  The  inner  tube  of 
the  system  is  connected  by  means  of  a  copper  tube 
with  the  Natterer  receiver  /,  which  contains  liquid 
ethylene.  The  temperature  of  the  liquefying  tube 
is  lowered  by  the  evaporation  of  this  liquid  under 
reduced  pressure.  The  liquid  ethylene,  before 
entering  the  system  of  tubes,  passes  through  a  cop- 
per coil,  surrounded  by  ether  and  solid  carbonic 
acid,  in  the  chamber  m.  By  the  evaporation  of  the 
liquid  ethylene,  under  a  pressure  of  10  mm.  of 
mercury,  the  temperature  sank  below  —  1 50°. 

The  working  of  the  apparatus  is  very  simple. 
After  the  temperature  has  been  lowered  to  about 
—  1 50°,  the  gas  is  compressed  in  the  tube  a  by 
means  of  the  vessel  z,  which  contains  the  gas 


I56 


LIQUEFACTION    OF   GASES 


under  high  pressure.     The  condensation  to  liquid 
begins  in  a  very  short  time. 

The  experiments  which  have  been  carried  out 
with  this  apparatus  have  been  published  in  numer- 
ous articles.  In  I8841  a  series  of  observations 
were  made  on  the  critical  temperature  and  press- 
ure of  nitrogen,  and  on  the  temperature  obtained 
by  the  evaporation  of  liquid  ethylene  and  nitrogen 
under  reduced  pressure.  The  results  obtained  with 
ethylene  are  as  follows  :  — 


Pressure 

Temperature 

750  mm.  of  mercury 

-I03° 

107         «           " 

-  II5-5 

3i         "           " 

-  139 

9.8         «           " 

-  i50-4 

The  temperatures  obtained  by  the  evaporation 
of  liquid  nitrogen  are  :  — 


Pressure 

Temperature 

35  atmospheres 

-I46° 

17 

-   1  60 

i          " 

-  194.4  (boiling  point) 

In  vacuo 

-  213 

1  Compt.  rend.,  99,  p.  133. 


EXPERIMENTS    OF   OLSZEWSKI  157 

A  few  months  later  he  made  use  of  liquid  air l 
as  a  refrigerant,  and  measured  the  temperatures 
obtained  under  different  pressures. 


Pressure 


Temperature 


39  atmospheres 
14 

4 

i  " 

In  vacuo 


140°  (critical  point) 

146 

176 

191.4  (boiling  point) 

205 


Solidification  of  Gases 

In  carrying  out  the  experiments  at  low  temper- 
atures, Olszewski  succeeded  in  solidifying  a  num- 
ber of  gases,  and  in  measuring  their  melting 
points.  In  i8842  he  evaporated  liquid  carbon 
monoxide  under  reduced  pressure,  and  obtained  a 
very  low  temperature.  At  a  pressure  of  one  at- 
mosphere the  temperature  was  —  190°;  this  rep- 
resents the  boiling  point  of  carbon  monoxide.  By 
reducing  the  pressure  as  far  as  possible  the  tem- 
perature sank  to  —  211°,  and  the  substance  solidi- 
fied to  an  opaque  mass. 

Early  the  next  year  a  series  of  similar  experi- 
ments were  made  with  nitrogen.3  At  a  tempera- 

1  Compt.  rend.,  99,  p.  184.  2Ibid.,  p.  706. 

3  Ibid.,  100,  p.  350, 


i58 


LIQUEFACTION   OF   GASES 


ture  of  —  214°  the  substance  solidified  to  an 
opaque  mass.  By  evaporating  the  resulting  solid 
under  a  pressure  of  4  mm.  of  mercury  the  tem- 
perature sank  to  —225°. 

During  the  same  year  methane  and  nitric  oxide 
were  evaporated  under  reduced  pressure.1  The 
former  gas  solidified  at  a  temperature  of  —  185°. 8. 
At  this  temperature  the  vapor-pressure  was  80 
mm.  of  mercury.  When  the  pressure  was  re- 
duced to  5  mm.  the  temperature  sank  to  —201°.  5. 
Nitric  oxide  solidified  at  a  temperature  of  —  167°. 
Under  a  pressure  of  18  mm.  of  mercury  a  tem- 
perature of  —i  76°. 5  was  obtained. 


Substance 


Freezing  Point 


Chlorine 

Hydrochloric  acid 

Hydrofluoric  acid 

Phosphine 

Arsine 

Stibine 

Ethylene 

Silicon  tetrafluoride  2 

Hydrogen  selenide  3 


—  102° 

-  116 
-92-3 

-  133 

-91.5 
-169 

-  102 

-68 


1  Compt.  rend.,  loo,  p.  940. 

2  Silicon  tetrafluoride  does  not  melt,  but  sublimes  into  a  gas  at 
the  ordinary  pressure. 

8  Phil.  Mag.,  39,  p.  210. 


EXPERIMENTS   OF    OLSZEWSKI  159 

Olszewski  also  solidified  a  number  of  other 
gases 1  some  of  which  had  been  liquefied  many 
years  before.  The  freezing  points  are  given  in 
the  preceding  table. 

Ethane  and  Propane  remained  liquid  at  a  tem- 
perature of  —  151°. 

In  1885  Olszewski  made  use  of  liquid  air  as  a 
refrigerant.2  By  evaporating  this  liquid  under 
a  very  low  pressure,  a  temperature  of  —  220°  was 
obtained.  An  account  is  also  given  in  this  article 
of  the  condensation  of  a  mixture  of  two  volumes 
of  hydrogen  with  one  volume  of  oxygen  to  a  color- 
less liquid  which  formed  in  thin  layers. 

Densities  and  Boiling  Points  of  Liquid  Methane \ 

Nitrogen,  and  Oxygen 

In  1886  methane,  oxygen,  and  nitrogen3  were 
liquefied  by  means  of  the  apparatus  described  on 
page  154.  A  series  of  observations  were  then 
made  on  the  densities  of  these  liquids  at  their  boil- 
ing points.  The  following  results  were  obtained  :  — 


Liquid 

Density 

Methane 
Oxygen 

Nitrogen 

0.415  (mean  of  3  determinations) 
i.i24(  "6  "  ) 
0.885  (  "4  "  ) 

1  Wien.  Monatshefte  fur  Chem.,  5,  p.  127;   Wien.  Ber.,  94,  p.  209. 

2  Compt.  rend.,  101,  p.  238.  8  Wied.  Ann.,  31,  p.  58. 


160  LIQUEFACTION   OF   GASES 

The  following  boiling  points  were  also  deter- 
mined :  — 


Liquid 

Boiling  Point 

Methane 

-I64° 

Oxygen 

-  181.4 

Nitrogen 

-  1944 

Carbon  monoxide 

—   IQO 

Nitric  oxide 

~  153 

These  temperatures  were  measured  by  means 
of  a  hydrogen  thermometer. 

Liquefaction  of  Ozone 

Olszewski  repeated  the  experiments  of  Haute- 
feuille  and  Chappuis  on  the  liquefaction  of  ozone, 
with  a  view  of  determining  the  boiling  point.1  The 
ozone  was  prepared  by  -means  of  Siemens'  appara- 
tus. In  order  to  obtain  the  liquid  in  a  static  con- 
dition under  a  pressure  of  one  atmosphere,  liquid 
oxygen  was  used  as  the  refrigerant.  The  appa- 
ratus previously  described  was  employed  in  this 
experiment. 

At  the  temperature  of  boiling  oxygen  (—  i8i°.4), 
the  ozone  condensed  to  a  dark  blue  liquid.  In 
layers  of  two  millimetres  in  thickness  the  liquid 

1  Wied.  Ann.,  37,  p.  337. 


EXPERIMENTS   OF   OLSZEWSKI  161 

appeared  opaque.  The  liquid  oxygen  which  sur- 
rounded the  tube  of  ozone  was  evaporated  under 
reduced  pressure  with  a  view  of  solidifying  the 
ozone.  The  experiment,  however,  was  unsuccess- 
ful. The  boiling  point  was  determined,  and  found 
to  be  —  1 06°.  The  liquid  is  somewhat  explosive, 
especially  when  brought  into  contact  with  liquid 
ethylene. 

Apparatus  for  the  Liquefaction  of  Gases  on  a 
Large  Scale 

According  to  the  earlier  observations  of  Olszew- 
ski  it  appears  that  liquid  oxygen  is  a  better  refrig- 
erant than  liquid  air  or  nitrogen.  In  order  that 
this  liquid  might  be  used  as  a  refrigerant  in  the 
liquefaction  of  other  gases,  the  author  constructed 
an  apparatus  by  means  of  which  oxygen  can  be 
liquefied  on  a  comparatively  large  scale.  This 
apparatus  was  constructed  in  1890,  and  enlarged 
during  the  same  year.1  A  section  of  the  enlarged 
apparatus  is  shown  in  figure  30. 

The  gas  is  liquefied  in  the  steel  cylinder  a,  of 
about  200  cc.  capacity.  The  upper  end  of  this  cyl- 
inder is  connected  by  means  of  a  small  copper 
tube  with  a  metallic  manometer  b,  and  an  iron 
vessel  c  of  10  litres  capacity.  The  vessel  c  con- 

1  Phil.  Mag.  [5],  39,  p.  192. 


162 


LIQUEFACTION   OF   GASES 


tains  dry  air  or  oxygen  under  a  pressure  of  100 
atmospheres.  The  lower  end  of  the  cylinder  a  is 
connected  by  means  of  a  copper  tube  with  the 
screw-cock  d,  which  serves  as  an  outlet  for  the 


FIG.  30. 

liquid  oxygen  or  air.  The  double-  or  triple-walled 
glass  vessel  m  which  surrounds  the  cylinder  a  is 
connected  with  the  reservoir  f,  which  contains 
liquid  ethylene,  and  with  an  exhaust-pump,  by 
means  of  the  tube  /.  The  liquid  ethylene,  before 


EXPERIMENTS   OF   OLSZEWSKI  163 

entering  the  vessel  m,  passes  through  the  chamber 
gt  which  contains  a  mixture  of  solid  carbonic  acid 
and  ether.  The  temperature  of  this  mixture  is 
lowered  still  further  by  connecting  the  tube  n  with 
an  exhaust-pump.  The  method  of  operation  is  as 
follows :  - 

The  pressure  in  the  chamber  g  is  first  lowered 
to  50  mm.  of  mercury.  The  vessel  m  is  then 
brought  into  communication  with  the  exhaust- 
pump  and  the  reservoir  of  liquid  ethylene.  The 
ethylene  eva-porates  rapidly  at  first,  but  finally  col- 
lects as  a  liquid  in  the  vessel  m.  As  soon  as  the 
liquid  ethylene  completely  surrounds  the  vessel  a, 
the  supply  is  cut  off.  When  the  temperature  is 
lowered  to  the  critical  temperature  of  the  gas  con- 
tained in  the  vessel  c,  communication  is  estab- 
lished between  this  vessel  and  the  cylinder  a. 
The  gas  enters  the  cooled  cylinder  under  a  press- 
ure indicated  by  the  manometer  b,  and  soon 
begins  to  liquefy.  The  manometer,  during  the 
condensation,  shows  a  constant  fall,  and  becomes 
stationary  only  when  the  cylinder  a  is  completely 
filled  with  liquid.  When  this  is  accomplished  the 
vessel  c  is  closed,  and  the  liquid  oxygen  or  air  is 
allowed  to  pass  out  through  the  cock  d  into  the 
double-  or  triple-walled  glass  vessel  e,  after  which 
the  process  may  be  repeated. 

The   temperatures   in   these    experiments  were 


164  LIQUEFACTION   OF  GASES 

not  measured  directly,  but  were  calculated  from 
the  pressure  under  which  the  liquid  ethylene  was 
allowed  to  evaporate.  This  pressure  was  meas- 
ured by  means  of  the  metallic  vacuometer  k. 

With  this  apparatus  Olszewski  obtained  200 
cubic  centimetres  of  liquid  air,  and  even  larger 
quantities  of  liquid  oxygen.  In  the  earlier  experi- 
ments it  was  thought  that  the  liquid  oxygen  was 
colorless,  but  when  obtained  in  a  larger  quantity  it 
was  found  to  be  pale  blue  in  color. 

The  Critical  Constants  and  Boiling  Point  of 
Hydrogen 

In  1891  Olszewski1  made  another  series  of 
experiments  with  hydrogen.  The  apparatus  em- 
ployed was  a  modification  of  that  represented  in 
figure  30.  Liquid  oxygen  and  liquid  air  were 
used  as  refrigerants  in  these  experiments.  The 
author  was  unable  to  obtain  any  indications  of  a 
meniscus  of  liquid  hydrogen,  but  on  allowing  the 
gas  to  expand  at  very  low  temperatures  signs  of 
ebullition  were  observed.  Moreover,  when  the 
hydrogen  was  allowed  to  expand  slowly  from 
pressures  of  80,  90,  100,  no,  120,  and  140  atmos- 
pheres, the  phenomenon  of  ebullition  always 
appeared  at  a  pressure  of  20  atmospheres.  From 

1  Phil.  Mag.  [5],  39,  p.  199. 


EXPERIMENTS   OF   OLSZEWSKI  165 

these  observations  Olszewski  concluded  that  20 
atmospheres  represent  the  critical  pressure  of 
hydrogen. 

In  order  to  test  the  accuracy  of  this  method  of 
determining  the  critical  pressure  of  a  gas,  the 
experiments  were  extended  to  oxygen  and  ethy- 
lene.  The  critical  pressure  of  oxygen  had  already 
been  measured,  and  found  to  be  50.8  atmospheres. 
To  determine  the  same  constant  by  the  expansion 
method,  the  gas  was  cooled  to  a  temperature  of 
about  1 6°. 3  above  the  critical  point,  and  then 
allowed  to  slowly  expand.  In  every  case  the 
meniscus  and  signs  of  ebullition  appeared  at  a 
pressure  of  about  5 1  atmospheres,  provided  the 
initial  pressure  was  not  lower  than  80  atmos- 
pheres. The  author  concluded,  from  his  ex- 
periments on  oxygen  and  ethylene,  that  critical 
pressures  can  be  determined  very  closely  by 
means  of  the  expansion  method. 

A  few  years  later 1  the  author  endeavored  to 
measure  the  temperature  of  the  hydrogen  at  the 
moment  of  expansion.  For  this  purpose  a  very 
sensitive  platinum  resistance  thermometer  was 
employed.  The  thermometer  was  previously  com- 
pared with  a  hydrogen  thermometer  at  temper- 
atures varying  from  o°  to  —  208°. 5.  When  this 

1  Phil.  Mag.  [5],  40,  p.  202. 


166  LIQUEFACTION   OF  GASES 

comparison  had  once  been  made  it  was  a  sim- 
ple matter  to  calculate  temperatures  lower  than 
—  208°. 5.  The  following  results  were  obtained:  — 


Expansion  of  Hydrogen  from  a  High 
Pressure  to 

Temperature 

20  atmospheres  (critical  pres.) 

10               " 

i          « 

—  234°.  5  (critical  temperature) 

-239  -7 
-243  .5  (boiling  point) 

The  experiments  were  then  extended  to  oxygen, 
which  was  allowed  to  expand  at  a  temperature  of 
about  1 6°  above  the  critical  point.  The  critical 
temperature  of  oxygen  determined  in  this  way  was 
found  to  be  — 118°  to  —119°. 2,  and  the  boiling 
point  —  i8i°.4  to  —182°. 5.  The  corresponding 
values  measured  directly  with  a  hydrogen  ther- 
mometer are  —  n8°.8  and  —  i8i°.4  to  —182.7, 
respectively. 

Olszewski  concluded,  from  these  observations, 
that  the  critical  temperature  of  hydrogen  is  about 
-  234°. 5,  and  the  boiling  point  —  243°. 5.  These 
values  agree  very  closely  with  those  obtained  theo- 
retically by  Natanson.1 

In  connection  with  the  experiments  which  have 
been  outlined,  Olszewski  also  made  numerous  ex- 
periments on  the  properties  of  liquefied  gases,  and 

1  Phil.  Mag.  [5],  40,  p.  272,  1895. 


EXPERIMENTS    OF   DEWAR  167 

on  the  properties  of  matter  in  general  at  low  tem- 
peratures. These  investigations  were  carried  out, 
for  most  part,  in  collaboration  with  his  colleague 
Witkowski.  The  observations  of  Olszewski  on 
argon  and  helium  will  be  considered  in  Section  IV 
of  this  chapter. 

EXPERIMENTS  OF  DEWAR 

Reference  has  already  been  made  to  the  experi- 
ments of  Dewar  on  the  liquefaction  of  gaseous 
mixtures,  and  the  determination  of  their  critical 
constants.  These  observations  were  made  in  1880. 
Four  years  later  he  extended  his  experiments  to 
the  so-called  permanent  gases,  and  constructed  an 
apparatus  for  demonstrating  the  liquefaction  of 
oxygen  in  the  lecture  room.1  The  essential  parts 
of  the  apparatus  are  shown  in  figure  31.  The  gas 
to  be  liquefied  is  contained  in  the  iron  reservoir  C 
under  a  pressure  of  150  atmospheres.  This  res- 
ervoir is  connected  with  the  manometer  D,  and 
also,  by  means  of  the  small  copper  tube  /,  with 
the  liquefying  tube  F.  The  pressure  is  regulated 
by  means  of  the  screw-cock  A.  The  liquefying 
tube  is  placed  in  the  glass  tube  G,  which  con- 
tains liquid  ethylene,  solid  carbonic  acid,  or  liquid 
nitrous  oxide.  This  tube  rests  in  a  larger  glass 

lProt.  Koy.  Inst.,  1884,  p.  148  ;   Phil.  Mag.  [5],  18,  p.  2io. 


1 68 


LIQUEFACTION   OF   GASES 


tube,  with  which  it  communicates  through  the 
opening  E.  The  outer  tube  is  connected  with  a 
Bianchi  exhaust-pump,  so  that  the  liquid  ethylene, 
etc.,  can  be  evaporated  under  reduced  pressure. 


FIG.  31. 

The  pressure  under  which  the  evaporation  takes 
place  is  measured  by  means  of  the  gauge  J. 

The  oxygen,  at  the  temperature  obtained  by  the 
evaporation  of  liquid  ethylene  under  a  pressure  of 
25  millimetres  of  mercury,  could  easily  be  lique- 


EXPERIMENTS   OF  DEWAR  169 

fied  at  a  pressure  of  from  20  to  30  atmospheres. 
When  liquid  nitrous  oxide  or  solid  carbonic  acid 
were  used  as  refrigerants,  it  was  necessary  to 
make  use  of  the  sudden  expansion  of  the  gas  to 
lower  the  temperature  still  further.  This  was 
accomplished  by  increasing  the  pressure  in  the 
liquefying  tube  to  80  atmospheres,  and  then  open- 
ing the  screwcock  B. 

This  method  was  thoroughly  satisfactory  for 
demonstrating  the  liquefaction  of  oxygen.  The 
liquefying  tube  was  only  about  five  millimetres 
in  diameter,  and  hence  only  small  quantities  of 
liquid  could  be  obtained.  The  tube  filled  with 
liquid  oxygen  (for  projection)  contained  about  1.5 
cubic  centimetres.  Some  rough  observations  were 
also  made  on  the  density  of  liquid  oxygen. 

In  1886  Dewar1  published  an  account  of  an 
apparatus  by  means  of  which  oxygen,  air,  etc., 
can  be  liquefied  on  a  much  larger  scale.  A  sec- 
tion of  the  apparatus  is  represented  in  figure  32. 
The  chamber  b  contains  a  mixture  of  solid  car- 
bonic acid  and  ether.  Ethylene  is  conducted  into 
the  tube  a,  where  it  is  liquefied  by  means  of  th'e  low 
temperature  produced  by  the  carbonic  acid.  This 
liquid  passes  from  the  coiled  tube  into  the  cham- 
ber d,  which  is  surrounded  by  a  larger  vessel  con- 

lProc.  Roy.  Inst.,  1886,  p.  550. 


LIQUEFACTION   OF   GASES 


^  a    taining  solid  carbonic 
acid  and  ether.     The 
liquid  ethylene  evapo- 
rates into   the  space 
between      the       two 
chambers.    A  contin- 
uous    copper     tube, 
about    forty-five   feet 
in  length,  passes  first 
through      the     outer 
vessel,       and       then 
through   the   chamber   con- 
taining liquid  ethylene.     A 
very   low   temperature    can 
be  produced  in  this  way. 

When  the  temperature 
0  has  been  lowered,  as  de- 
scribed above,  perfectly  dry 
oxygen  gas  is  introduced 
into  the  copper  tube  under 
a  pressure  of  about  75  at- 
mospheres. The  pressure 
gauge  (not  represented  in 
the  figure)  soon  indicates 
the  beginning  of  liquefaction 
in  the  tube.  The  valve  A  is 
then  opened  and  the  liquid 
oxygen  rushes  out  into  the 


FIG.  32. 


EXPERIMENTS    OF   DEWAR  171 

glass  tube  g  which  is  immersed  in  the  liquid 
ethylene  contained  in  the  tube  /.  In  the  first  ex- 
periments about  22  cubic  centimetres  of  liquid 
oxygen  were  obtained  in  the  tube.  In  order  to 
reduce  the  temperature  as  far  as  possible,  the 
tubes  g  and  i  were  each  connected  with  an  exhaust- 
pump.  A  temperature  of  about  —  200°  was  thus 
obtained.  During  this  process  a  white  deposit 
was  formed  in  the  tube  gy  which  was  supposed, 
then,  to  be  solid  oxygen.  Later,  however,  the 
author  observed  that  these  white  particles  of  solid 
matter  were  due  to  impurities. 

Having  constructed  an  apparatus  for  liquefying 
oxygen,  air,  etc.,  in  considerable  quantity,  Dewar 
extended  his  observations  on  the  properties  of 
liquefied  gases,  and  the  properties  of  matter  in 
general  at  low  temperatures.  In  1892  he  pub- 
lished an  account  of  some  observations  on  the 
magnetic  properties  of  liquid  oxygen.1  Becquerel 
was  the  first  to  call  attention  to  this  property  of 
oxygen.  He  experimented  with  charcoal  which 
was  saturated  with  oxygen  gas.  In  1849  Faraday 
noticed  that  oxygen  is  strongly  magnetic  in  com- 
parison with  other  gases.  Dewar  observed  that  if 
liquid  oxygen  is  placed  between  and  a  little  below 
the  poles  of  an  electro-magnet,  the  liquid  will  rise 

1  Proc.  Roy.  Inst.,  13,  p.  695. 


172  LIQUEFACTION    OF   GASES 

to  the  poles  when  the  circuit  is  completed.  The 
magnetic  moment  of  liquid  oxygen,  he  says,  is 
about  1000,  when  the  magnetic  moment  of  iron  is 
taken  as  1,000,000.  When  liquid  air  was  placed 
between  the  poles  of  the  magnet,  all  of  the  liquid 
was  drawn  to  the  poles,  and  there  was  no  separa- 
tion of  oxygen  and  nitrogen. 

The  absorption  spectrum  of  liquid  oxygen  was 
also  examined,  and  found  to  be  the  same  as 
that  of  the  gas.  Both  the  liquid  and  the  highly 
compressed  gas  show  .a  series  of  five  absorption 
bands,  situated  respectively  in  the  orange,  yellow, 
green,  and  blue  of  the  spectrum.  Some  experi- 
ments were  also  made  on  chemical  action  at  low 
temperatures.  Reference  will  be  made  to  these 
observations  in  the  conclusion  at  the  end  of  the 
volume. 

During  the  next  year  Dewar  announced  that  he 
had  succeeded  in  freezing  ordinary  air  into  a  clear, 
transparent  solid.1  This  experiment  is  of  consider- 
able importance,  inasmuch  as  neither  oxygen  nor 
air  had  been  solidified  previous  to  this  time. 

The  Dewar  Vacuum  Bulbs 

In  1893,  Dewar2  made  an  important  contribu- 
tion to  the  researches  at  low  temperatures  by  the 

1  Chem.  News,  67,  p.  126.  2  Proc.  Roy.  Inst.,  14,  p.  I. 


EXPERIMENTS    OF   DEWAR 


173 


introduction  of  a  vessel  for  storing  such  volatile 
fluids  as  liquid  oxygen,  liquid  air,  etc.  These 
liquids,  and  other  similar  liquids,  which  had  been 
obtained  previous  to  this  time,  could  be  kept  only 
a  few  minutes  in  the  open 
air  owing  to  the  rapid 
evaporation.  Experimen- 
ters had  already  retarded 
the  evaporation  to  some 
extent  by  the  use  of 
double-walled  vessels. 
Dewar  conceived  the  idea 
of  exhausting  the  air  from 
the  space  between  the 
walls  of  such  vessels. 

Figure  33  represents 
one  of  these  bulbs.  The 
outer  vessel  is  exhausted 
to  a  very  high  degree, 
and  then  sealed  off  at 
the  lower  end.  This  pre- 
vents, to  a  considerable 
extent,  the  convective  transference  of  'heat  from 
the  outer  air  to  the  liquid  air  in  the  inner  vessel. 

To  test  the  efficiency  of  this  form  of  vessel, 
comparisons  were  made  with  similar  vessels  which 
had  not  been  exhausted.  The  comparisons  were 
based  upon  the  amount  of  liquid  oxygen  or  liquid 


FIG.  33. 


174 


LIQUEFACTION   OF   GASES 


ethylene  evaporated  in  a  given  time.  The  vessels 
were  placed  in  water  which  was  kept  at  constant 
temperature.  The  results  were  as  follows  :  — 


Amount  of  Gas  Evolved 


Liquid  oxygen  surrounded  by  a  vacuum 

chamber 

Liquid  oxygen  surrounded  by  an  air 

chamber 

Liquid  ethylene  surrounded  by  a  vacuum 

chamber 

Liquid  ethylene  surrounded  by  an  air 

chamber 


170  cc.  per  mm. 
840      «         « 
56      "        « 
250       «        « 


From  these  observations  it  is  evident  that  the 
rate  of  evaporation  from  the  air  bulbs  is  about  five 
times  that  from  the  vacuum  bulbs.  By  covering 
the  inner  vessel  with  a  thin  deposit  of  silver,  the 
rate  of  evaporation  is  reduced  to  less  than  one  half 
of  that  given  in  the  table.  Liquid  oxygen  or  liquid 
air  can  be  kept  for  several  hours  in  such  vessels 
under  the  ordinary  atmospheric  pressure. 

The  next  step  was  to  construct  a  series  of 
vacuum  vessels  of  different  forms  which  could 
be  employed  in  experiments  of  different  nature. 
Figure  34  represents  a  few  of  the  many  forms  of 
these  vessels  which  have  been  constructed.  Dewar 
and  other  experimenters  have  made  use  of  these 


EXPERIMENTS   OF   DEWAR 


175 


bulbs  for  investigating  the  properties  of  matter  at 
low  temperatures,  and  for  determining  the  proper- 
ties and  physical  constants  of  liquefied  gases. 

In  1894  Dewar  determined  the  thermal  trans- 
parency of  some  liquefied  gases  for  heat  of  high 


FIG.  34. 

refrangibility.1  Taking  chloroform  as  the  unit  of 
comparison,  and  correcting  for  differences  in  the 
refractive  indices,  the  results  are  as  follows  :  — 

Chloroform i.o. 

Carbon  disulphide 1.6 

Liquid  oxygen 0.9 

Liquid  nitrous  oxide 0.93 

Liquid  ethylene 0.60 

Ether 0.50 


1  Proc.  Roy.  Inst.,  14,  p.  393. 


176  LIQUEFACTION   OF   GASES 

Notwithstanding  the  low  temperatures,  liquid 
oxygen  and  nitrous  oxide  are  very  transparent  to 
high  temperature  radiation. 

The  author  suggested  in  this  article  that,  instead 
of  silvering  the  inner  bulbs  of  the  vacuum  vessels, 
it  is  better  to  leave  a  small  quantity  of  mercury  in 
the  vacuum  chambers.  When  liquid  air  is  intro- 
duced into  the  inner  bulbs,  a  thin  coating  of  solid 
mercury  is  found  on  the  outer  surface. 

A  series  of  observations  were  also  made  on 
the  breaking  stress  of  metals  at  low  tempera- 
tures. The  following  table  contains  the  breaking 
stress,  in  pounds,  for  metallic  wires  of  0.098  in.  in 

diameter :  — 

15°  -182° 

Steel  (soft) 420  700 

Iron 320  670 

Copper     ...'....  200  300 

Brass 310  440 

German  silver 470  600 

Gold 255  340 

Silver 330  420 

The  breaking  stress  of  wires  is  not  changed 
by  cooling  down  to  —  182°,  and  then  allowing  the 
temperature  to  rise. 

In  1895  Dewar  made  use  of  a  different  form 
of  apparatus  in  the  liquefaction  of  gases.1  This 
apparatus  involves  the  regenerative  principle  in 

1  Proc.  Roy.  Inst.,  15,  p.  133. 


EXPERIMENTS    OF   DEWAR  177 

the  method  of  refrigeration,  and  belongs  more 
properly  to  the  next  section  (see  p.  197). 

By  means  of  this  apparatus  liquid  air,  etc.,  can 
be  obtained  in  a  very  short  time,  and  at  a  com- 
paratively small  expense.  By  placing  a  litre  of 
liquid  air  in  a  globular  vacuum  bulb  and  subject- 
ing it  to  exhaustion,  the  author  states  that  as  much 
as  half  a  litre  of  solid  air  can  be  obtained  and 
maintained  in  the  solid  condition  for  a  period  of 
half  an  hour.  An  examination  of  the  solid  showed 
it  to  be  a  "  nitrogen- jelly  "  containing  liquid  oxygen. 

After  obtaining  liquid  air,  oxygen,  and  nitrogen 
in  considerable  quantities,  Dewar  made  an  elabo- 
rate series  of  experiments  on  their  densities.  The 
method  consisted  in  weighing  different  substances 
of  known  specific  gravities  in  the  liquids.  More 
than  twenty  substances  were  weighed  in  liquid 
oxygen,  and  corrections  made  for  the  contraction 
of  the  solids.  The  mean  of  the  results  gave  a 
value  of  1.1375  for  the  density  of  liquid  oxygen. 
By  weighing  a  large  silver  ball  in  liquid  air  and 
liquid  nitrogen,  the  densities  of  the  liquids  were 
found  to  be  0.910  and  0.850  respectively. 

In  1897  Dewar  constructed  an  apparatus  for  the 
examination  of  the  least  condensible  portion  of 
air.1  From  the  experiments  with  this  apparatus 

1  Chem.  News,  76,  p.  272. 


178  LIQUEFACTION  OF   GASES 

the  author  concluded  that  every  gas  which  occurs 
in  the  atmosphere  either  condenses  to  the  liquid 
state,  or  is  soluble  in  liquid  air. 

Numerous  observations  have  been  made  by 
Dewar  and  Fleming  on  the  electric  conductivity 
of  metals,  and  the  dielectric  constant  of  organic 
liquids  at  low  temperatures.1 

The  experiments  of  Dewar  on  the  liquefaction 
of  gases  since  1895  will  be  considered  in  the  next 
two  sections. 

EXPERIMENTS  OF  KAMERLINGH-ONNES 

During  the  last  few  years  Kamerlingh-Onnes 
has  been  experimenting  on  the  liquefaction  of 
gases.  The  apparatus  which  is  used  by  him  at 
present  in  the  liquefaction  of  oxygen  is  somewhat 
similar  to  that  employed  by  Pictet  in  1877.  The 
complete  operation  consists  of  three  cycles,  as 
follows : 2  — 

First  Cycle.  Liquid  methyl  chloride  surrounds 
a  tube  containing  ethylene  under  pressure.  The 
vessel  which  contains  the  methyl  chloride  is  con- 
nected with  an  exhaust-pump,  by  means  of  which 
the  pressure  is  considerably  reduced.  The  rapid 
evaporation  of  the  liquid  lowers  the  temperature 

1  A  list  of  references  to  these  observations  has  been  compiled  by 
Dickson.  —  Phil.  Mag.  [5],  45,  p.  528,  1898. 

2  Zeit.  fur  conipr.  und fliiss.  Gase,  I,  p.  169,  1898. 


EXPERIMENTS   OF   KAMERLINGH-ONNES    179 

of  the  chamber,  and  hence,  of  the  ethylene.  The 
vapors  of  methyl  chloride  which  pass  out  of  the 
vessel  are  compressed,  by  means  of  a  second 
pump,  in  a  chamber  where  they  finally  condense 
to  a  liquid.  This  liquid  passes  back  again  to  the 
vessel  which  surrounds  the  ethylene  tube,  thus 
making  the  cycle  complete. 

Second  Cycle.  This  cycle  is  similar  to  the  first. 
The  compressed  ethylene  is  liquefied  by  means  of 
the  low  temperature  which  results  from  the  evapo- 
ration of  the  methyl  chloride.  The  liquid  ethylene 
is  conducted  into  a  tube,  where  it  surrounds  a 
smaller  tube  containing  compressed  oxygen  gas. 
The  liquid  ethylene  is  connected  with  an  exhaust- 
pump,  and  evaporated  under  reduced  pressure. 
The  resulting  vapors  are  recondensed,  and  the 
cycle  is  made  complete. 

Third  Cycle.  In  this  cycle  the  oxygen  is  con- 
densed to  the  liquid  state.  The  oxygen  tube  is 
connected  with  both  an  exhaust  and  a  compression 
pump.  The  liquid  ethylene,  boiling  under  reduced 
pressure,  lowers  the  temperature  of  the  compressed 
oxygen  to  --  140°,  when  it  condenses  to  a  liquid. 
By  means  of  the  pumps  the  liquid  oxygen  is 
removed  to  a  carefully  protected  reservoir.  The 
operation  consists  of  three  complete  cycles,  and 
hence  is  continuous. 

A  section  of   the   apparatus   is   shown   in   the 


i8o  LIQUEFACTION   OF   GASES 

article  to  which  reference  has  already  been  made. 
The  drawing,  however,  is  rather  complicated,  and 
for  that  reason  has  not  been  reproduced  here.  By 
means  of  this  apparatus  the  author  has  obtained 
liquid  oxygen  in  considerable  quantity. 


SECTION   III 

LIQUEFACTION  OF  GASES  BY  THE  REGENERATIVE 
METHOD 

So  far,  the  low  temperatures  necessary  for  the 
liquefaction  of  gases  have  been  obtained  mainly 
by  the  evaporation,  especially  under  reduced  press- 
ure, of  liquid  carbonic  acid,  liquid  nitrous  oxide, 
liquid  ethylene,  liquid  air,  etc.  A  different  method 
of  lowering  the  temperature  has  become  of  consid- 
erable importance  in  recent  years.  The  gas  which 
is  to  be  liquefied  is  compressed  to  a  very  high 
pressure  ;  the  heat  due  to  the  compression  is  re- 
moved by  means  of  water,  and  the  gas  is  then 
allowed  to  expand.  In  this  way  exceedingly  low 
temperatures  can  be  obtained.  With  this  method 
the  gas  to  be  liquefied  is  the  only  substance,  apart 
from  the  apparatus,  which  is  necessary  for  carry- 
ing out  the  experiment.  The  process  is  frequently 
referred  to  as  the  self-intensification^  or  the  regen- 
erative, method. 


REGENERATIVE   METHOD  181 

The  history  of  this  method  is  rather  interesting. 
According  to  Joule,1  Dr.  Cullen  and  Dr.  Darwin 
were  the  first  to  observe  that  the  temperature  of  a 
gas  is  lowered  by  rarefaction  and  increased  by 
compression.  They  experimented  with  ordinary 
air.  Dalton  succeeded  in  measuring  this  change 
of  temperature  with  some  degree  of  accuracy  (see 
p.  12).  In  1806  Gay  Lussac  (p.  12)  made  a  series 
of  experiments  on  the  changes  of  temperature 
which  accompany  the  compression  and  rarefaction 
of  gases.  Thilorier  (1834)  observed  that  carbonic 
acid  could  be  solidified  by  means  of  its  own  expan- 
sion (p.  38).  In  1845  Joule,  and  later  Joule  and 
William  Thomson,  made  a  very  exhaustive  study  of 
these  phenomena,  both  experimentally  and  theo- 
retically. Mayer,  Rankine,  and  Clausius  have  also 
contributed  largely  to  this  subject.  Further  refer- 
ence to  these  investigations  will  be  made  in  the  theo- 
retical considerations  which  will  be  taken  up  later. 

In  connection  with  these  and  many  other  similar 
observations  which  were  conducted  solely  for  scien- 
tific purposes,  a  number  of  experiments  have  also 
been  made  with  a  view  of  applying  this  method  of 
lowering  the  temperature  for  refrigerating  pur- 
poses. In  1849  Dr.  John  Gorrie2  constructed  an 

1  Phil.  Mag.  [3],  26,  p.  369. 

-  Wallis-Tayler,  Refrigerating  and  Ice-Making  Machinery, 
p.  116. 


1 82  LIQUEFACTION   OF   GASES 

ice  machine,  based  upon  the  compression  and 
expansion  of  air.  In  1857  Siemens1  constructed 
a  refrigerating  machine,  which  he  describee  as 
follows :  — 

"  The  invention  relates  to  freezing  and  refriger- 
ating by  the  expansion  of  air  or  elastic  fluid.  The 
air  is  first  compressed  by  a  cylinder,  or  by  pumps 
of  any  suitable  construction,  by  which  the  temper- 
ature is  raised,  and  it  is  cooled  while  in  the  com- 
pressed state,  and  is  then  allowed  to  expand  in  a 
cylinder  or  engine  of  any  suitable  construction,  by 
which  the  temperature  is  lowered.  The  air  thus 
cooled  is  brought  in  contact  with  the  articles  to  be 
cooled  or  frozen,  and  is  then  conducted  through  an 
interchanger,  or  apparatus,  by  which  it  is  made  to 
cool  the  compressed  air  which  enters  the  inter- 
changer  in  the  opposite  direction.  .  .  .  The  prin- 
ciple of  the  invention  is  adapted  to  produce  an 
accumulated  effect,  or  an  indefinite  reduction  of 
temperature."  Kirk  in  1863,  Marchant  in  1869, 
and  Giffard  and  Postle  in  1873,  constructed  ice 
machines  in  which  the  freezing  was  produced  by 
the  expansion  of  air.2  In  1885  Solvay  3  described 
a  method  which  is  similar  to  that  of  Siemens.  A 


1  Linde,  Engineer,  82,  p.  486. 

2  Wallis-Tayler,    Refrigerating    and    Ice-Making    Machinery, 
p.  116  et  seq. 

3  Linde,  Engineer,  82,  p.  486. 


REGENERATIVE   METHOD  183 

very  efficient  refrigerating  machine,  based  upon 
this  same  principle,  was  constructed  by  Wind- 
hausen.1  Reference  might  be  made  to  other  ma- 
chines of  a  similar  nature,  but  it  is  not  within  the 
scope  of  a  book  of  this  kind  to  consider  the  subject 
of  refrigerating  machines.  Those  who  are  inter- 
ested in  that  branch  of  the  work  can  refer,  in  con- 
nection with  the  various  text-books  and  journals 
on  engineering,  to  Wallis-Tayler's  Refrigerating 
and  Ice-Making  Machinery,  and  especially  to  the 
two  journals  Ice  and  Refrigeration,  published  in 
New  York  and  Chicago,  and  the  Zeitschrift  fiir  die 
gesammte  Katie-Industrie,  published  in  Leipzig. 

The  preceding  examples,  however,  are  sufficient 
to  show  that  the  lowering  of  temperature,  which 
accompanies  the  expansion  of  a  gas,  was  observed 
a  century  ago,  and  that  this  method  of  lowering 
the  temperature  has  been  applied  technically  for  at 
least  fifty  years.  The  method  is  not  new. 

In  1874  Edwin  J.  Houston2  suggested  a  form  of 
apparatus  which  is  very  similar  to  the  machines 
employed  at  present  in  the  liquefaction  of  air. 
The  following  are  his  words :  "  The  means  of 
obtaining  exceedingly  low  temperatures  seem  at 
last  to  have  been  fulfilled  in  the  '  Windhausen  Ice 
and  Refrigerating  Machine.'  Though  introduced 

1  Houston,  Jour.  Frank.  Inst.,  67,  p.  10. 

2  ibid.,  p.  9,  1874- 


184  LIQUEFACTION   OF   GASES 

for  practical  purposes,  mainly  for  the  cheap  pro- 
duction of  artificial  ice,  the  machine  contains  latent 
possibilities,  which  we  hope  will  at  once  be  utilized, 
that  open  up  the  most  promising  field  to  the  origi- 
nal investigator,  and  bid  fair  to  enrich  science  with 
stores  of  new  facts." 

" .  .  .  In  the  Windhausen  process,  a  steam 
engine  is  employed  to  compress  the  air  to  2  or  3 
atmospheres.  The  heat  developed  by  the  com- 
pression is  drawn  off  during  the  passage  of  the 
condensed  air  through  pipes  in  a  series  of  cham- 
bers, in  which  cold  water  is  flowing.  The  cooled 
air  is  then  allowed  to  expand  into  a  cylinder  un- 
der gradually  diminishing  pressure,  the  expansion 
being  attended  with  the  development  of  great 
cold." 

".  .  .  The  following  modifications  of  the  ap- 
paratus would  render  its  cold-producing  power 
almost  unlimited :  — 

"i.  A  communication  between  the  expansion 
cylinder  and  the  chambers  through  which  the  con- 
densed air  is  conducted  before  it  is  allowed  to 
expand.  Supposing  this  outlet  regulated  by  a 
cock,  a  blast  of  very  cold  air  could  replace  the  run- 
ning water,  and  reduce  the  compressed  air  to  a 
very  low  temperature. 

"  2.  The  introduction  of  a  second  compressing 
cylinder,  with  which  the  compressed  air,  after  be- 


REGENERATIVE   METHOD  185 

ing  cooled,  could  be  still  further  compressed,  again 
cooled,  and  finally  conducted  into  the  expansion 
cylinder.  Under  a  pressure  of,  say,  60  atmos- 
pheres, a  considerable  mass  of  air  at  the  tempera- 
ture of,  say,  —i  00°  F.  would,  in  its  expansion, 
produce  a  reduction  of  temperature  greater  per- 
haps than  any  yet  obtained.  .  .  .  There  would 
appear  to  be  no  other  limit  to  the  reduction  of 
temperature  save  what  would  arise  from  the 
strength  of  materials,  or  the  liquefaction  and  sub- 
sequent freezing  of  the  nitrogen,  or  the  oxygen  of 
the  air,  or  of  the  air  itself. 

"  Among  the  advantages  that  we  may  rationally 
expect  to  accrue  from  the  apparatus  thus  modified 
are  the  following  :  — 

"  i.  The  confirmation  or  otherwise  of  the  '  abso- 
lute zero '  as  determined  by  the  expansion  or 
contraction  of  gases,  by  heat  or  cold. 

"  2.  The  liquefaction  and  subsequent  solidifica- 
tion of  many  of  the  incoercible  gases,  the  determi- 
nation of  their  physical  peculiarities  as  liquids  or 
solids,  together  with  their  crystalline  form. 

"3.  The  action  of  intense  cold  on  the  chemical 
affinities  of  certain  gaseous  compounds. 

"4.  The  action  of  intense  cold  on  the  color  of 
certain  chemical  compounds." 

These  predictions  have  been  thoroughly  fulfilled. 
In  the  apparatus  suggested,  Houston  anticipated 


186  LIQUEFACTION   OF  GASES 

the  methods  which  were  employed  twenty  years 
later  in  the  liquefaction  of  air  by  Linde,  Hampson, 
and  Tripler. 

In  1875  Coleman1  constructed  an  apparatus  for 
the  liquefaction,  on  a  large  scale,  of  some  very 
volatile  hydrocarbons.  The  lowering  of  the  tem- 
perature was  produced  by  the  expansion  of  the 
compressed  gases.  The  machine  involves  :  — 

"  i.  The  pumping  of  the  gas  by  steam  power 
into  a  system  of  tubes  capable  of  being  externally 
cooled,  and  from  which  condensed  liquids  can  be 
drawn  off  by  ball-cocks. 

"  2.  Employing  the  compressed  gas,  after  being 
deprived  of  its  liquid,  for  working  a  second  engine 
coupled  with,  and  parallel  to,  the  first,  thus  receiv- 
ing a  portion  of  the  force  originally  employed  in 
the  compression. 

"  3.  Employing  the  expanded  gas,  after  having 
had  its  temperature  reduced  in  the  act  of  doing 
the  work  of  pumping,  for  supplying  the  necessary 
cold  for  cooling  a  portion  of  the  condenser  pipes 
to  zero." 

The  cycle  of  operations  was  complete.  The 
temperature  of  the  compressed  gas  was  about  5°, 
while  the  minimum  temperature  after  expansion 
was  —45°.  With  this  apparatus  a  continuous 

1  Chem.  News,  39,  p.  87. 


EXPERIMENTS    OF   LINDE  187 

stream  of  the  liquefied  gas  could  be  produced. 
About  250,000  gallons  of  the  liquid  hydrocarbons 
were  produced  during  the  first  three  years. 

Cailletet  and  Pictet  have  also  made  use  of  the 
expansion  of  gases  as  a  means  of  lowering  the 
temperature,  but  in  their  work  the  regenerative 
principle  was  not  used.  Wroblewski,  Olszewski, 
and  Dewar,  previous  to  1895,  made  experiments 
of  a  similar  nature.  Reference  has  already  been 
made  to  these  observations.  In  1894  Kamerlingh- 
Onnes  made  use  of  the  regenerative  principle  in 
the  liquefaction  of  gases.1  Omitting  a  number  of 
observations  on  the  compression  and  expansion  of 
gases,  which  have  but  slight  bearing  on  the  conden- 
sation of  gases,  we  may  proceed  at  once  to  the  con- 
sideration of  some  forms  of  apparatus  which  have 
recently  been  constructed  for  the  purpose  of  lique- 
fying oxygen,  nitrogen,  and  especially  ordinary  air. 

APPARATUS  EMPLOYED  BY  LINDE  IN  THE 
LIQUEFACTION  OF  AIR 

This  apparatus  is  an  outgrowth  of  a  long  expe- 
rience in  the  construction  of  refrigerating  ma- 
chines. We  may  omit  these  devices,  however, 
and  proceed  at  once  to  the  consideration  of  the 
apparatus  employed  in  the  liquefaction  of  air. 

1Ref.  Dewar,  Proc.  Roy.  InsL,  15,  p.  133. 


188  LIQUEFACTION   OF   GASES 

The  apparatus  was  successfully  operated  in 
May,  1895,  and  was  constructed  as  follows  : l  The 
general  arrangement  of  the  apparatus  is  shown  in 
figure  35.  The  air  to  be  liquefied  is  brought  by 
means  of  the  compressor  C  to  a  pressure  of  about 
200  atmospheres  (in  the  first  few  experiments  the 
pressure  employed  was  about  65  atmospheres).  R 
is  a  water-cooler,  which  serves  to  remove  the  heat 
of  compression.  The  compressed  air  then  passes 
through  the  concentric  tube-system  Ht  which  is 
placed  in  a  large,  well-insulated  chamber,  to  the 
expansion  valve  r,  where  it  is  allowed  to  escape 
into  the  receiver  G.  The  sudden  expansion  of  the 
air  produces  a  considerable  lowering  of  tempera- 
ture. The  cold  air  rushes  out  of  the  receiver,  and 
passes  up  through  the  outer  tube,  thus  lowering 
the  temperature  of  the  compressed  air  in  the  inner 
tube.  As  the  process  continues  the  temperature 
gradually  falls  until  the  air  begins  to  liquefy  in  the 
receiver  G.  This  takes  place  at  the  temperature 
of  boiling  air  ;  consequently,  the  liquid  air  is  ob- 
tained in  a  static  condition  at  the  ordinary  atmos- 
pheric pressure. 

In  this  way  Linde  obtained  liquid  air  in  consider- 
able quantity.  The  resulting  liquid  was  very  rich  in 
oxygen,  inasmuch  as  tfte  boiling  point  of  oxygen  is 

1  Engineer,  82,  p.  4861 


EXPERIMENTS    OF   LINDE 


189 


higher  than  that  of  nitrogen.    The  author  modified 
the  apparatus  somewhat  in  order  to  obtain  a  more 
complete  separation  of  the  oxygen  and  nitrogen.1 
The    apparatus    employed   at   present2    differs 


1  Engineer,  82,  p.  509.     The  efficiency  and  theory  of  the  appa- 
ratus are  also  considered  by  Linde  in  this  article. 

2  Zeit.  f.  Eleklrochem.,  4,  p.  4,   1897  5    a^so  Zeit.   Compr.  und 
fttiss.  Case,  I,  p.  117,  1897. 


190 


LIQUEFACTION   OF   GASES 


somewhat  from  that  just  described.  The  general 
arrangement  of  this  apparatus  is  shown  in  figure 
36.  The  tube-system  in  this  case  consists  of  three 


FIG.  36. 

concentric  copper  tubes,  arranged  in  the  form  of 
a  spiral.  The  coils  are  placed  in  a  carefully  in- 
sulated chamber.  By  means  of  the  compressor 
d,  the  air  is  forced  into  the  innermost  tube  of  the 


EXPERIMENTS    OF    LINDE  191 

system  under  a  pressure  of  about  200  atmos- 
pheres. The  heat  of  compression  is  removed  by 
means  of  the  water-cooler  G.  The  small  tube  is 
provided  with  an  expansion  valve  at  a,  where  the 
air  is  allowed  to  expand  into  the  space  between 
innermost  and  middle  tubes.  In  this  operation 
the  air  passes  from  a  pressure  of  200  atmospheres 
to  a  pressure  of  16  atmospheres.  The  tempera- 
ture, of  course,  is  greatly  reduced  by  the  sudden 
expansion  of  the  air.  The  cold  air  passes  up 
through  the  middle  tube,  and  finally  back  to  the 
compressor  d,  where  it  is  again  compressed  to 
200  atmospheres.  This  process  can  be  seen  from 
the  directions  of  the  arrows.  The  compressor  e 
maintains  a  pressure  of  16  atmospheres  in  the 
middle  tube.  As  the  process  continues,  the  tem- 
perature gradually  becomes  lower.  The  middle 
tube  is  provided  with  an  expansion  valve  at  b, 
similar  to  that  at  a,  through  which  the  air  is  al- 
lowed to  expand  a  second  time.  In  this  case,  the 
air  passes  from  a  pressure  of  16  atmospheres  into 
the  space  between  the  outer  and  middle  tubes, 
where  the  pressure  is  one  atmosphere.  This 
operation  lowers  the  temperature  still  further. 
The  cold  air  passes  up  through  the  outer  tube  of 
the  system,  abstracting  heat  from  the  compressed 
air,  and  finally  escapes  through  the  outlet  at  the 
top  of  the  chamber.  The  apparatus  is  so  adjusted 


192  LIQUEFACTION   OF   GASES 

that  the  compressor  e  supplies  sufficient  air  to 
exactly  replace  the  small  quantity  which  is  lost. 
The  cycle  is  now  complete,  and  the  temperature 
of  the  system  gradually  decreases.  When  the  pro- 
cess has  continued  for  a  period  of  from  \\  to  2 
hours,  liquid  air  begins  to  collect  in  the  bottom 
of  the  chamber,  and  passes  into  the  double-walled 
Dewar  bulb  c.  The  liquid  can  be  drawn  from  this 
vessel  by  opening  the  stop-cock  //.  About  one 
litre  of  liquid  air  can  be  produced  per  hour,  with 
a  three  horse-power  engine.  With  a  larger  ap- 
paratus, and  a  correspondingly  increased  power, 
the  liquid,  of  course,  could  be  obtained  in  much 
larger  quantities.  Numerous  observations  have 
also  been  made  by  this  experimenter  on  the  prop- 
erties of  matter  at  low  temperatures. 

Linde  has  in  the  process  of  construction,  for 
the  Rhenania  Chemical  works  at  Aix-la-Chapelle, 
a  liquid  air  plant  with  a  capacity  of  about  50  litres 
of  liquid  air  per  hour,  and  -an  expenditure  of  about 
1 20  horse-power.1 

HAMPSON'S  APPARATUS  FOR  THE  LIQUEFACTION 
OF  GASES 

The  apparatus  employed  by  Hampson  in  the 
liquefaction  of  oxygen,  air,  etc.,  is  based  upon  the 

1  Ewing,  Engineering,  65,  p.  310,  1898. 


EXPERIMENTS    OF    HAMPSON 


193 


same  principle  as 
that  employed  by 
Linde,  which  has  just 
been  described.  Con- 
siderable discussion 
has  arisen  concern- 
ing this  form  of  ap- 
paratus as  to  priority 
of  invention.  Hamp- 
son's  patent  is  dated 
May  23,  1895.  With 
this  statement  as  to 
the  date  of  the  inven- 
tion, we  may  leave 
the  question  of  pri- 
ority and  proceed  at 
once  with  a  descrip- 
tion of  the  apparatus. 
A  longitudinal  sec- 
tion of  the  apparatus1 
is  represented  in 
figure  37.  The  gas 
to  be  liquefied  (oxy- 
gen, air,  etc.)  is  in- 
troduced through  the 
small  tube  at  the 

1  Engineer,    8l,   p.   310, 
1896. 

o 


194  LIQUEFACTION   OF   GASES 

upper  end  under  a  pressure  of  120  atmospheres. 
The  gas  enters  the  apparatus  at  the  ordinary  tem- 
perature (the  heat  of  compression  having  been 
removed).  The  tube  through  which  the  gas  is 
introduced  extends  downward  in  the  form  of  a 
spiral  around  a  central  column.  At  the  lower 
end  of  the  spiral  is  an  expansion  valve  which 
opens  from  above  by  means  of  a  screw.  The 
expanded  gas  passes  up  through  the  apparatus 
and  out  again  at  the  upper  end.  The  outer  por- 
tions of  the  apparatus  are  carefully  packed  with 
felt. 

The  details  of  the  spiral  tube  and  expansion 
valve  are  shown  in  figure  38.  The  coil  A  ter- 
minates in  the  jet-piece  D,  which  delivers  the  gas 
against  a  flat  plug  on  the  screw  C.  A  slightly 
different  form  of  valve  is  shown  in  the  small 
figure  to  the  left.  The  gas  on  escaping  through 
this  valve  expands  to  a  pressure  of  one  atmos- 
phere. The  temperature  of  the  gas  is  consider- 
ably reduced  in  consequence  of  this  expansion. 
The  cold  gas  passes  up  around  the  coil  as  shown 
by  the  arrows  in  the  figure,  thus  lowering  the 
temperature  of  the  compressed  gas.  This  makes 
the  process  self-intensifying.  As  the  operation 
continues  the  temperature  gradually  falls,  until 
finally  the  gas  begins  to  liquefy.  Liquid  oxygen 
and  liquid  air  can  be  obtained  in  this  way  in  a 


EXPERIMENTS    OF   HAMPSON 


195 


static  condition  at  the  ordinary  atmospheric  press- 
ure in  a  comparatively  short  time.     The  apparatus 
was       constructed       on 
rather  a  small  scale,  and 
had  a  capacity  of  about 
two    cubic    centimetres 
of    liquid     oxygen    per 
minute. 

During  the  next  year 
the  apparatus  was  some- 
what modified.1  The  air 
in  this  case  was  intro- 
duced under  a  pressure 
of  87  atmospheres.  The 
jet  of  liquid  air  could 
be  seen  within  twenty- 
five  minutes,  and  the 
liquid  air  began  to  col- 
lect in  the  receiver 
within  thirty-three  min- 
utes from  the  beginning 
of  the  operation.  A 
vacuum  vessel  was  used  FIG.  38. 

as  the  receiver. 


1  Engineer ;  83,  p.  294. 


196  LIQUEFACTION   OF   GASES 

APPARATUS    EMPLOYED    BY   DEWAR   IN   THE 
LIQUEFACTION  OF  GASES 

On  the  1 9th  of  December,  1895,  Dewar  read  a 
paper  before  the  English  Chemical  Society  on  the 
"  Liquefaction  of  Air  and  Researches  at  Low 
Temperature." 1  In  this  paper  the  author  de- 
scribes an  apparatus  in  which  the  self-intensifica- 
tion method  of  refrigeration  is  employed.  The 
compressed  gas  is  cooled  to  about  —  80°  by  means 
of  liquid  carbonic  acid,  and  then  allowed  to  ex- 
pand under  a  regenerative  coil.  A  section  of  the 
apparatus  is  shown  in  figure  39. 

The  carbonic  acid  is  introduced  into  the  appara- 
tus at  B,  and  passes  through  the  coiled  tube  re- 
presented by  the  shaded  circles.  C  is  a  carbonic 
acid  valve,  and  H  the  carbonic  acid  outlet.  The 
air  or  oxygen  to  be  liquefied  enters  the  apparatus 
at  A,  under  a  pressure  of  150  atmospheres.  D  is 
a  regenerative  coil,  and  F  an  expansion  valve 
where  the  compressed  gas  is  allowed  to  expand 
into  the  vacuum  vessel  G. 

When  the  temperature  of  the  system  is  lowered  to 
about  —80°,  the  gas  is  allowed  to  expand  through 
the  valve  F.  This  produces  a  further  decrease 
in  the  temperature.  The  cooled  gas  passes  up 
around  the  regenerative  coil  and  lowers  the  tem- 

1  Proc.  Roy.  Inst.,  15,  p.  133. 


EXPERIMENTS   OF   DEWAR 


197 


FIG.  39. 


198  LIQUEFACTION   OF   GASES 

perature  of  the  compressed  gas.  The  temperature 
of  the  system  falls  rapidly,  and  within  fifteen 
minutes  from  the  time  of  starting,  liquid  air  (or 
whatever  the  substance  may  be)  begins  to  drop 
into  the  vacuum  vessel  G.  By  means  of  this 
apparatus  Dewar  was  able  to  liquefy  oxygen,  air, 
etc.,  on  a  comparatively  large  scale. 

Dewar  also  made  a  number  of  experiments  on 
"  gas  jets  containing  liquid."  In  these  observa- 
tions a  small  regenerative  coil  was  placed  in  a  long 
vacuum  vessel.  Three  different  forms  of  these 
vessels  were  constructed.  The  compressed  gas 
was  allowed  to  expand  from  the  coil  near  the 
lower  end  of  the  vacuum  tube.  Oxygen  under  a 
pressure  of  100  atmospheres,  and  previously  cooled 
to  —79°,  produced  a  visible  jet  of  liquid.  Dewar 
suggests  this  method  as  a  very  rapid  means  of 
obtaining  low  temperatures. 

Similar  experiments  were  made  with  hydrogen. 
When  cooled  to  —  200°  and  allowed  to  expand  from 
a  pressure  of  140  atmospheres  in  one  of  these 
tubes,  no  liquid  jet  could  be  seen.  If  the  gas  con- 
tained a  few  per  cent  of  oxygen  the  liquid  jet  be- 
came visible.  By  allowing  the  pure  hydrogen  to 
expand  from  the  pressure  of  200  atmospheres  over 
a  longer  regenerative  coil,  which  has  been  previously 
cooled  to  —  200°,  the  liquid  jet  becomes  visible. 
The  liquid  hydrogen,  however,  could  not  be  ob- 


EXPERIMENTS   OF   TRIPLER  199 

tained  in  a  static  condition.  To  obtain  some  idea 
of  the  temperature  of  the  liquid  jet,  the  author 
placed  some  liquid  air  and  liquid  oxygen  in  the 
lower  end  of  the  tube.  Within  a  few  minutes 
about  fifty  cubic  centimetres  of  these  liquids  were 
transformed  into  hard,  white  solids,  resembling 
avalanche  snow.  The  solid  oxygen  had  a  pale 
bluish  color,  and  showed  by  reflection  all  the 
absorption  bands  of  the  liquid. 

TRIPLER'S  APPARATUS  FOR  THE  LIQUEFACTION 
OF  AIR 

The  method  employed  by  Tripler  in  the  lique- 
faction of  air  is  based  upon  the  same  principle  as 
that  employed  by  Linde  and  Hampson,  but  is 
operated  on  a  much  larger  scale.  Unfortunately 
no  thoroughly  scientific  account  of  this  apparatus 
has  yet  been  published.  The  temperature  is  low- 
ered by  expanding  highly  compressed  air  in  a 
long  tube  under  a  regenerative  coil.  The  general 
plan  of  the  apparatus  is  shown  in  figure  4O.1 

The  steam  boiler  b  supplies  steam  to  the  com- 
pressor c  under  a  pressure  of  about  85  pounds  per 
square  inch.  The  compressor  is  provided  with 
three  air  cylinders  arranged  in  tandem  on  the 
same  rod.  These  cylinders  are  cooled  by  means 

1  Engineering  A'eivs,  39,  p.  246,  1898. 


200 


LIQUEFACTION   OF   GASES 


EXPERIMENTS   OF   TRIPLER  201 

of  water-jackets.  The  first  or  low-pressure  cylin- 
der is  10^  inches  in  diameter,  and  compresses  the 
air  to  a  pressure  of  about  4  atmospheres.  The 
second  or  intermediate  cylinder  is  6J  inches  in 
diameter,  and  increases  the  pressure  to  about  25 
atmospheres.  The  third  or  high-pressure  cylinder 
is  2|  inches  in  diameter,  and  delivers  the  air  at 
a  pressure  of  about  150  atmospheres.  The  air 
is  taken  into  the  compressor  from  the  outside 
through  the  pipe  a,  which  is  provided  with  a  dust- 
separator  at  d.  The  heat  of  compression  is  re- 
moved by  means  of  the  water  in  the  tank/.  Af- 
ter leaving  the  cooler  the  compressed  air  passes 
through  the  separator  s,  which  removes  the  last 
traces  of  moisture. 

The  air  is  now  ready  to  be  liquefied.  This  is 
accomplished  by  means  of  the  two  liquefiers  m 
and  11.  These  liquefiers  consist,  in  each  case,  of  a 
long  coil  of  copper  tubing  with  an  expansion  valve 
at  the  lower  end.  The  coils  are  carefully  pro- 
tected from  the  external  heat  by  means  of  felt. 
The  air  enters  these  liquefiers  under  a  pressure 
of  1 50  atmospheres,  and  is  allowed  to  expand  to  a 
pressure  of  one  atmosphere.  The  temperature  is 
considerably  reduced  by  this  expansion ;  the  cold 
air  passes  up  around  the  coil  and  lowers  the  tem- 
perature of  the  compressed  air,  and  thus  the  influ- 
ence becomes  accumulative.  Within  about  twenty 


202  LIQUEFACTION   OF   GASES 

minutes  the  air  begins  to  liquefy  in  the  lower 
end  of  the  tube.  The  liquid  air  is  removed  by 
means  of  the  valves  at  the  lower  ends  of  the 
liquefiers. 

As  operated  at  present  this  apparatus  has  a 
capacity  of  from  three  to  four  gallons  of  liquid  air 
per  hour.  Tripler  has  obtained  liquid  air  on  a 
much  larger  scale  than  have  any  of  the  other 
experimenters.  It  is  not  an  uncommon  occur- 
rence to  ship  liquid  air  from  this  plant  (in  ten- 
gallon  cans)  to  a  distance  of  several  hundred 
miles.  The  liquid  has  been  successfully  trans- 
ported from  New  York  to  Philadelphia,  Wash- 
ington, Boston,  and  other  cities.  This  plant  has 
made  it  possible  to  experiment  with  liquid  air  in 
both  technical  and  scientific  lines  at  a  compara- 
tively small  expense. 

THEORY  OF  THE  SELF-INTENSIFICATION  METHOD 
OF  REFRIGERATION 

An  elaborate  discussion  of  this  problem  necessi- 
tates the  use  of  complicated  mathematical  formulae, 
and  would  be  out  of  place  in  a  work  of  this  nature. 
For  that  reason  the  subject  will  be  considered 
only  in  a  general  way.1  It  has  been  known  for 

1  For  a  more  complete  discussion,  see  Joule  and  Thomson, 
Trans.  Roy.  Soc.,  144,  p.  321,  or  some  work  on  thermodynamics. 


THEORY  OF  REGENERATIVE  METHOD  203 

more  than  a  century  that  when  a  gas  is  compressed, 
the  temperature  rises,  and,  conversely,  when  the 
compressed  gas  is  allowed  to  expand,  the  tempera- 
ture falls.  In  1842  Mayer  investigated  the  cause 
of  these  thermal  changes.  "Whence  comes  the 
heat,"  he  asks,  "  generated  during  the  compression 
of  a  gas,  and  what  becomes  of  the  heat  which  van- 
ishes when  the  gas  expands  ?  "  He  considered  the 
problem  in  the  light  of  the  conservation  of  energy. 
The  work  which  is  done  in  the  compression  of  a 
gas,  he  says,  is  changed  into  heat,  and  the  work 
which  is  done  by  the  expanding  gas,  against  the 
external  pressure,  cannot  spring  into  existence 
from  nothing,  but  comes  from  the  heat  which  the 
gas  loses.  Mayer's  conception  implies  that  heat 
is  a  form  of  energy.  He  fully  recognized  the  fact 
that  heat  can  be  obtained  from  or  transformed 
into  other  forms  of  energy. 

In  order  to  make  this  subject  clear,  it  will  be 
necessary  to  consider  the  two  specific  heats  of 
gases.  By  the  specific  heat  of  a  substance  is 
meant  the  capacity  of  unit  mass  of  the  substance 
for  heat ;  i.e.  the  ratio  of  the  amount  of  heat  sup- 
plied to  the  body  to  the  rise  in  temperature. 
When  a  gas  is  heated,  either  the  pressure  or 
volume  is  increased.  If  the  pressure  of  a  gas 
is  kept  constant  during  a  specific  heat  determina- 
tion, the  value  obtained  is  greater  than  that  ob- 


204  LIQUEFACTION   OF  GASES 

tained  at  constant  volume.  In  the  former  case  the 
gas  expands  against  a  definite  pressure ;  i.e.  it  per- 
forms a  certain  amount  of  mechanical  work.  The 
excess  of  heat  required  to  raise  the  temperature  of 
a  gas  at  constant  pressure  over  that  required  at 
constant  volume  is  simply  the  amount  of  energy 
required  in  the  expansion  of  the  gas. 

According  to  this  theory  there  should  be  no 
temperature  change  when  a  gas  is  allowed  to  ex- 
pand into  a  vacuum,  as  there  is  no  external  work 
to  overcome.  The  experiments  of  Gay  Lussac 
and  those  of  later  experimenters  have  shown  this 
to  be  true.1  Moreover,  if  the  theory  of  Mayer  is 
true,  the  difference  between  the  quantities  of  heat 
necessary  to  raise  the  temperature  of  one  gram 
of  air  through  one  degree  under  the  two  condi- 
tions; i.e.  at  constant  pressure  and  constant  vol- 
ume, should  correspond  to  the  work  performed  in 
expanding  one  gram  of  air  ^\^  of  its  volume  at 
o°.  Both  of  these  values  have  been  determined. 
The  first  is  0.0692  calories  of  heat,  and  the  second 
2923.5  gram  centimetres  of  work.  If,  then,  0.0692 
calories  of  heat  correspond  to  2923.5  gram  centi- 


1  Strictly  speaking,  this  statement  is  true  only  in  the  case  of  a 
perfect  gas.  Although  there  is  no  external  work  to  overcome  when 
ordinary  gases  expand  into  a  vacuum,  a  small  quantity  of  energy 
is  required  to  overcome  the  molecular  attraction.  This  causes  a 
slight  decrease  in  the  temperature. 


THEORY   OF   REGENERATIVE    METHOD     205 
metres  of  work,  one  calorie  of  heat  corresponds  to 

,      =  42245  gram  centimetres  of  work.     This 
0.0692 

latter  value,  being  equivalent  to  one  calorie,  is 
called  the  mechanical  or  dynamical  equivalent  of 
heat,  and  agrees  very  closely  with  the  values 
obtained  by  different  methods  by  Joule,  Rowlands, 
and  others.  We  may  safely  assume,  then,  that 
the  heat  which  is  absorbed  when  a  compressed 
gas  is  allowed  to  expand  is  equivalent  to  the 
external  work  performed. 

In  order  to  calculate  the  decrease  in  tempera- 
ture which  accompanies  the  expansion  of  a  gas,  it 
is  necessary  to  know  the  specific  heat  of  the  gas 
at  constant  pressure  and  constant  volume  ;  also 
the  initial  and  final  pressures  of  the  gas. 

Suppose  a  small  quantity  of  heat,  dQ,  be  com- 
municated to  a  gas  at  constant  volume,  and  let  the 
rise  in  temperature  be  represented  by  dT.  Then, 
as  no  external  work  has  been  done, 


where  Cv  represents  the  specific  heat  of  the  gas  at 
constant  volume.     Equation  (i)  may  be  written 


If  the  pressure  p  had  remained  constant  when  the 
heat  was  communicated,  there  would  have  been  a 


206  LIQUEFACTION   OF   GASES 

slight  increase  in  volume  which  we  may  represent 
by  dv.  Then  a  certain  amount  of  external  work 
(pdv)  would  have  been  performed.  If  this  value 
is  represented  in  thermal  units,  the  available  heat 
for  increasing  the  temperature  of  the  gas  is  dQ 
—  pdv,  and  the  above  equation  becomes 

dQ-pdv=CvdT  (2) 

dQ      r    i  Pdv 

or  3^=6«+^F* 

dT  dT 

The  term  -^  in  this  case  represents  the  specific 
dl 

heat  of  the  gas  at  constant  pressure,  and  hence 

(3) 


where  Cp  is  the  specific  heat  at  constant  pressure. 
By  differentiating   the   equation  pv  —  R  T  with 
respect  to  v,  we  obtain 

pdv  =  RdT, 


or  ;       -  — 

hence  Cp=  Cv  +  R. 

If  the  equation  pv  =  RT  be  differentiated  with 
respect  to  all  of  the  variables,  we  have 

pdv  +  vdp  =  RdT. 


THEORY   OF    REGENERATIVE   METHOD      207 

Substituting  for  R    its  equivalent  Cp  —  Cv,  this 
equation  becomes 

pdv  +  vdp 


By  substituting  this  value  of  dT  in  2,  we  obtain 
dQ  =  ^pdv  +  ^vdp.  (4) 

If  the  gas  is  allowed  to  expand  adiabatically,1 
dQ  =  o,  and  hence,  from  4,  we  have 

£/«&  +  £„#  =  <>. 

Dividing  this  equation  by  -^,  we  obtain 


The  last  equation  may  be  written 


where  k  represents  the  ratio  of  the  specific  heat  of 
the  gas  at  constant  pressure  to  that  at  constant 
volume.  If  the  gas  be  allowed  to  assume  two 
definite  conditions  with  respect  to  pressure  and 
volume,  p,  v,  and  plt  vlt  and  we  integrate  equa- 

JA  gas  is  said  to  expand  adiabatically  when  no  heat  is  com- 
municated from  or  given  out  to  the  external  surroundings. 


208  LIQUEFACTION   OF   GASES 

tion  (5)  between  these  limits,  and   transpose  the 
result,  we  obtain 


log/  -  log/,  =  k  (log  t>,  -  log  z>), 

i 

i& 


"(*) 


—  /       \ 

10^) 

Simplifying  this,  we  have 

(6) 


Suppose  now  that  a  gas  be  allowed  to  expand 
from  the  pressure  /  to  the  pressure  /r  Before 
and  after  the  expansion  the  gas  must  fulfill  the 
equations  pv  —  RT,  and  p^\  —  RT^  respectively. 
Dividing  the  first  of  these  by  the  second,  we  have 

pv  _    T 
P\v\      Ti 

If   we  substitute   for  —   its   value   from  equa- 

»l 
tion  (6),  the  equation  becomes 


Knowing,  then,  the  initial  and  final  pressures, 
and  also  the  initial  temperature,  the  final  tempera- 
ture can  be  calculated  from  equation  (7). 

In  the  case  of  air,  k=  1.41.     Substituting  this 


THEORY  OF  REGENERATIVE  METHOD  209 

value,  and  assuming  the  initial  temperature  to  be 
zero  centigrade  and  the  final  pressure  to  be  one 
atmosphere,  the  theoretical  temperatures  obtained 
by  the  adiabatic  expansion  of  air  are  given  in  the 
following  table  :  — l 


Initial  Pressures 

Final  Temperatures 

TOO  atmospheres 

-  20I°.5 

200                 " 

-214  .5 

300         « 

—  221    .0 

400         " 

-225   .1 

500          " 

-  228  .2 

Applying  these  results  to  the  liquefaction  of 
gases  by  means  of  the  regenerative  coil,  it  is  evi- 
dent that  the  expansion  of  the  gas  in  the  tube 
lowers  the  temperature  by  an  amount  which  corre- 
sponds to  equation  (7).  Further,  the  issuing  jet 
experiences  a  much  greater  decrease  in  tempera- 
ture owing  to  the  greater  difference  between  the 
initial  and  final  pressures.  Finally,  the  expanded 
gas  of  very  low  temperature  passes  up  around 
the  coil  and  lowers  the  temperature  of  the  com- 
pressed gas  ;  i.e.  the  initial  temperature  of  the  gas, 
before  expansion,  gradually  decreases.  In  this 
way  the  influence  becomes  accumulative,  and  the 


1  Ostwald's  Outlines  of  General  Chemistry  t  p.  83. 
P 


210  LIQUEFACTION   OF   GASES 

process  has  been  termed  the  regenerative  or  self- 
intensifying  method. 

In  practice  the  efficiency  of  such  an  apparatus 
is  never  equal  to  the  theoretical.  In  the  first 
place,  there  is  always  an  inflow  of  heat  from  the 
outside.  Careful  insulation  may  reduce,  but  can 
never  entirely  eliminate,  this  influence.  Further- 
more, the  interchange  of  heat  between  the  ex- 
panded gas  and  the  counter-current  apparatus  is 
never  complete.1 

Rayleigh  suggests  that  the  efficiency  of  the  va- 
rious forms  of  apparatus  employed  at  present  in 
the  liquefaction  of  air  might  be  considerably  in- 
creased by  the  use  of  a  turbine.2  He  says :  "  It 
must  not  be  overlooked,  that  to  allow  the  work 
of  expansion  to  appear  as  heat  at  the  very  place 
where  the  utmost  cooling  is  desired,  is  very  bad 
thermodynamics.  The  work  of  expansion  should 
not  be  dissipated  within,  but  be  conducted  to  the 
exterior.  ...  A  turbine  of  some  sort  might  be 
used.  This  would  occupy  little  space,  and  even  if 
of  low  efficiency,  would  still  allow  a  considerable 
fraction  of  the  work  of  expansion  to  be  conveyed 
away.  The  worst  turbine  would  be  better  than 
none,  and  would  probably  allow  the  pressures  to 

1  For  details  in  regard  to  the  efficiency  of  the  apparatus,  see 
Linde,  Engineer,  82,  pp.  485  and  509. 

2  Nature,  58,  p.  199,  1898. 


THEORY  OF  REGENERATIVE  METHOD  211 

be  reduced.  It  should  be  understood  that  the  ob- 
ject is  not  so  much  to  save  the  work,  as  to  obviate 
the  very  prejudicial  heating  arising  from  its  dis- 
sipation in  the  coldest  part  of  the  apparatus.  It 
seems  to  me  that  the  future  may  bring  great 
developments  in  this  direction,  and  that  it  may 
thus  be  possible  to  liquefy  even  hydrogen  at  one 
operation." 

Since  the  regenerative  principle  has  proved 
successful  in  the  liquefaction  of  air,  it  has  been 
suggested  by  some  inventors  that  the  immense 
quantity  of  heat  which  is  stored  up  in  the  earth's 
atmosphere  may  be  obtained  as  available  energy 
for  doing  work  at  a  very  small  expense.  Their 
idea  is  that  there  is  considerably  more  energy 
stored  up  in  the  liquid  air  than  is  required  to 
produce  the  liquid  by  the  regenerative  method. 
Without  going  into  the  theory  of  this  suggestion, 
we  may  dispose  of  it  by  quoting  the  following  pas- 
sage from  Nernst :  — 

"  In  the  judgment  of  some  inventors  who  are 
completely  permeated  with  the  accuracy  of  the 
law  of  the  conservation  of  energy,  it  is  by  no 
means  regarded  as  impossible  to  construct  a  ma- 
chine which  should  be  able  to  furnish  work  as 
desired  and  free  of  cost.  External  work  and  heat 
are  equivalent  to  each  other.  Moreover,  energy 
in  the  form  of  heat  is  in  abundance,  so  that  it  only 


212  LIQUEFACTION   OF   GASES 

needs  an  apparatus  in  which  one  shall  apply  it  in 
driving  our  machine,  to  use  up  the  energy  of  its 
environments.  Such  an  apparatus,  for  example, 
might  be  sunk  into  a  great  water  reservoir,  whose 
enormous  quantity  of  energy  could  be  changed 
into  useful  work ;  it  would,  for  example,  make  the 
steam  engines  of  our  ocean  steamers  unnecessary, 
and  would  keep  the  screw  of  a  ship  in  motion  as 
long  as  desired,  and  at  the  cost  of  the  immeasur- 
able store  of  heat  in  the  sea.  Such  an  apparatus 
would  be  in  certain  respects  a  perpetual  motion, 
and  yet  not  contradictory  to  the  first  law  of  ther- 
modynamics, since  it  would  extract  the  heat  of  its 
environments  and  give  it  back  again  as  external 
work  which,  as  a  result  of  the  friction  of  the  screw, 
would  change  itself  back  again  into  heat,  to  enter 
the  cycle  anew. 

"  Unfortunately  such  an  apparatus,  which  would 
make  coal  worthless  as  a  source  of  energy,  ap- 
pears to  be  a  chimera,  exactly  as  was  the  per- 
petual motion  of  the  inventor  of  the  last  century ; 
at  least,  many  fruitless  attempts  have  made  this 
more  than  probable.  Thus,  as  we  sum  up  the 
numerous  abortive  endeavors,  we  come,  in  a  way 
analogous  to  that  which  led  to  the  knowledge  of 
the  conservation  of  energy,  to  the  proposition  that 
an  apparatus  which  could  continually  change  the 
heat  of  its  environments  into  external  work  is  a 


LIQUEFACTION   OF   ARGON  213 

contradiction  to  a  law  of  nature,  and  therefore  an 
impossibility.  Although  by  recognizing  this  law 
the  human  spirit  of  invention  may  be  poorer  by 
one  problem,  yet  natural  investigation  is  com- 
pensated for  it  by  a  principle  of  almost  unlimited 
application." 

SECTION   IV 

LIQUEFACTION   OF    ARGON,    HYDROGEN,    HELIUM, 
ETC. 

There  remain  to  be  considered  some  special 
observations  in  the  liquefaction  of  gases.  The 
quantity  of  gas  to  be  liquified,  in  some  cases,  was 
very  small,  and  hence  an  apparatus  of  special 
construction  was  necessary. 

Liquefaction  and  Solidification  of  Argon 

In  1895  Olszewski1  subjected  argon  to  low  tem- 
peratures and  high  pressures.  A  sample  of  the 
pure  dry  gas,  about  300  cc.,  was  obtained  from 
Ramsay.  Four  series  of  experiments  were  made  ; 
two  with  the  object  of  determining  the  critical 
temperature  and  pressure,  and  two  for  the  pur- 
pose of  determining  the  boiling  point  and  freezing 
point  under  atmospheric  pressure. 

1  Trans.  Roy.  Soc.,  186,  p.  253,  1895. 


214  LIQUEFACTION   OF   GASES 

In  the  first  two  experiments  use  was  made  of 
an  apparatus  similar  to  that  of  Cailletet.  Liquid 
ethylene,  boiling  under  reduced  pressure,  was  used 
as  the  refrigerant.  At  a  temperature  of  —  128°. 6 
and  a  pressure  of  38  atmospheres  the  argon  con- 
densed to  a  colorless  liquid.  On  slowly  raising 
the  temperature  the  meniscus  became  less  distinct 
and  finally  disappeared.  This  was  repeated  sev- 
eral times  with  a  view  of  determining  the  critical 
temperature  and  pressure.  The  mean  of  seven 
observations  gave  —  121°  for  the  critical  tem- 
perature, and  50.6  atmospheres  for  the  critical 
pressure.  The  vapor  pressure  of  argon  at  a 
temperature  of  —  139°.!  was  found  to  be  23.7 
atmospheres. 

The  experiments  on  the  boiling  and  freezing 
points  were  carried  out  by  means  of  the  apparatus 
represented  in  figure  41.  The  argon  was  con- 
tained in  the  glass  burette  b,  closed  at  both  ends 
with  glass  stop-cocks.  The  lower  end  of  the 
burette  was  connected,  by  means  of  a  flexible 
tube,  with  the  mercury  reservoir  a.  By  means  of 
the  mercury,  the  gas  could  be  transferred  to  the 
liquefying  tube  d,  which  was  immersed  in  the 
liquid  oxygen  contained  in  the  quadruple-walled 
glass  tube  e.  The  tube  i  was  connected  with  a 
large  air-pump,  and  the  tube  c  with  a  mercury 
air-pump. 


LIQUEFACTION   OF   ARGON 


215 


When  the  temperature  of  the  tube  d  had  be- 
come equal  to  that  of  liquid  oxygen  boiling  under 
the  ordinary  atmospheric  pressure,  the  argon  was 


FIG.  41. 


216  LIQUEFACTION   OF  GASES 

admitted,  but  showed  no  signs  of  liquefaction. 
This  showed  that  the  boiling  point  of  argon  is 
lower  than  that  of  oxygen.  The  pressure  of  the 
argon  was  then  adjusted  so  as  to  remain  equal  to 
that  of  the  atmosphere.  The  tube  containing  the 
liquid  oxygen  was  slightly  exhausted,  and  at  a 
temperature  of  —  187°  the  argon  began  to  liquefy. 
As  a  mean  of  four  experiments  Olszewski  gives 
—  187°  for  the  boiling  point  of  argon.  From  the 
volume  of  gas  used  and  the  volume  of  liquid  ob- 
tained, the  density  of  liquid  argon  at  the  boiling 
point  was  estimated  to  be  about  1.5. 

The  temperature  of  the  liquid  oxygen  was  then 
lowered  by  slow  exhaustion  to  —  191°,  when  the 
argon  solidified  to  a  crystalline  mass  resembling 
ice.  At  lower  temperatures  the  mass  became 
opaque.  The  substance  was  frozen  and  melted 
four  times.  The  mean  value  obtained  for  the 
melting  point  by  means  of  a  hydrogen  thermome- 
ter is  -  i89°.6. 

Experiments  ^vith  Helium 

In  1896  Olszewski1  made  an  extensive  series 
of  experiments  with  a  view  of  liquefying  helium. 
The  pressure  was  obtained  by  means  of  a  Caille- 
tet  apparatus.  The  liquefying  tube  of  this  appa- 

1  Wied.  Ann.,  59,  p.  184  ;   Nature,  54,  p.  377. 


EXPERIMENTS   WITH   HELIUM  217 

ratus  was  thoroughly  exhausted  by  means  of  a 
mercury  pump,  and  then  carefully  filled  with  dry 
helium  which  had  been  obtained  from  Ramsay. 
In  the  first  series  of  experiments  liquid  oxygen 
was  used  as  the  refrigerant.  By  the  evaporation 
of  this  liquid  under  a  pressure  of  10  mm.  of  mer- 
cury a  temperature  of  —  210°  could  be  obtained. 
At  this  temperature  and  under  a  pressure  of  125 
atmospheres  helium  showed  no  signs  of  liquefac- 
tion. The  gas  was  then  allowed  to  expand  until 
the  pressure  had  decreased  to  twenty  atmos- 
pheres, and  in  some  cases  to  one  atmosphere,  but 
there  was  no  evidence  of  condensation  to  the 
liquid  state. 

In  the  second  series  of  experiments  liquid  air 
was  employed  as  the  refrigerant.  By  the  evapora- 
tion of  liquid  air  under  a  pressure  of  10  mm. 
of  mercury  the  temperature  was  reduced  to  about 
—  220°.  Even  at  this  low  temperature  and  with 
a  pressure  of  140  atmospheres,  the  results  were 
all  negative.  Under  these  conditions  the  gas 
was  again  allowed  to  expand,  but  there  were  no 
indications  of  liquefaction.  The  author  says  :  "  In 
every  single  instance  I  have  obtained  negative 
results,  and,  as  far  as  my  experiments  go,  helium 
remains  a  permanent  gas,  and  apparently  much 
more  difficult  to  liquefy  than  even  hydrogen." 
The  experiments  were  carried  out  on  a  very  small 


2i8  LIQUEFACTION   OF   GASES 

scale,  owing  to  the  small  quantity  of  gas  at  hand 
(about  140  cc.). 

The  temperatures  were  not  measured  directly 
in  these  experiments,  but  were  calculated  by 
Olszewski  from  the  Laplace-Poisson  equation  for 
the  change  of  temperature  in  a  gas  during  adi- 
abatic  expansion.  According  to  this  equation  the 
temperature  of  the  gas  when  allowed  to  expand, 
as  previously  described,  to  a  pressure  of  one 
atmosphere,  is  about  -  264°.  It  seems  more 
probable,  however,  in  the  light  of  recent  investi- 
gations, that  the  temperature  was  somewhat  above 
this  point.  The  author  also  constructed  a  helium 
thermometer  and  compared  it  with  a  hydrogen 
thermometer  from  the  temperature  of  —  182°  to 
-210°.  The  results  obtained  by  the  two  ther- 
mometers agreed  very  closely. 

Liquefaction  of  Fluorine 

In  1895  Dewar  remarked  that  "  fluorine  is  the 
only  widely  distributed  element  in  nature  which 
has  not  been  liquefied."  Two  years  later,  how- 
ever, this  gas  was  condensed  to  the  liquid  state  by 
Moissan  and  Dewar.1  The  latter  experimenter  had 
previously  subjected  fluorine  to  low  temperatures 
with  a  view  of  liquefaction,  but  without  success. 

1  Compl.  rend.,  124,  p.  1202  ;  and  125,  p.  505,  1897. 


LIQUEFACTION   OF   FLUORINE  219 

The  fluorine  used  by  Moissan  and  Dewar  was 
prepared  by  the  electrolysis  of  potassium  fluoride 
dissolved  in  anhydrous  hydrofluoric  acid.  The 
acid  fumes  were  removed  by  conducting  the  gas 
through  a  platinum  coil,  which  was  surrounded 
by  a  mixture  of  solid  carbonic  acid  and  alcohol ; 
after  which  the  fluorine  was  conducted  through 
platinum  tubes  filled  with  perfectly  dry  sodium 
fluoride. 

The  apparatus 1  employed  in  the  liquefaction  is 
represented  in  figure  42.  The  glass  bulb  E  is 
fused  to  the  platinum  tube  A,  which  surrounds  a 
smaller  platinum  tube  D.  Each  of  these  tubes  is 
provided  with  a  screw-cock  so  that  the  communica- 
tion with  the  outer  air  or  the  current  of  fluorine 
can  be  interrupted  at  pleasure.  In  the  first  series 
of  experiments  the  glass  bulb  E  was  immersed  in 
liquid  oxygen,  which  was  contained  in  a  cylindrical 
vacuum  vessel.  At  the  temperature  of  boiling  air 
(about  —  183°)  the  fluorine  passed  through  the 
apparatus  without  showing  any  signs  of  liquefac- 
tion. By  evaporating  the  liquid  oxygen  under  re- 
duced pressure,  liquid  fluorine  soon  began  to  collect 
in  the  apparatus.  The  outlet  to  the  fluorine  tube 
was  then  closed,  and  the  glass  bulb  soon  became 
filled  with  a  clear  yellow,  extremely  mobile  liquid. 

1  Chem.  News,  76,  p.  261. 


220 


LIQUEFACTION   OF   GASES 


FIG.  42. 


At  this  temperature  fluorine  did 
not  attack  the  glass  bulb. 

The  experiment  was  repeated, 
using  freshly  prepared 
liquid  air  as  the  refrig- 
erant. At  a  tempera- 
ture of  -  190°  the 
fluorine  condensed  to 
the  liquid  state.  From  the  two 
series  of  experiments  the  authors 
calculated  the  boiling  point  to 
be  about  —  187°,  which  is  the 
same  temperature  as  that  ob- 
tained by  Olszewski  for  the 
boiling  point  of  argon.  The 
critical  temperature  was  esti- 
mated to  be  about  —  120°,  and 
the  critical  pressure  about  40 
atmospheres.  The  chemical 
activity  of  fluorine  was  greatly 
reduced  at  the  temperature  of 
boiling  oxygen.  At  this  tem- 
perature it  does  not  replace 
iodine,  and  is  without  action  on 
phosphorus,  boron,  silicon,  iron, 
etc.  With  hydrogen,  turpentine, 
and  benzene  it  reacts  with  incan- 
descence. 


LIQUEFACTION   OF   HYDROGEN  221 

The  density  of  liquid  fluorine  was  determined 
by  placing  solid  substances  of  different  specific 
gravities  in  the  liquid.  The  result  of  a  number  of 
observations  gave  a  density  of  1.14.  The  liquid 
is  soluble  in  all  proportions  in  liquid  oxygen  and 
liquid  air. 

The  authors  endeavored  to  reduce  the  tempera- 
ture to  the  freezing  point  of  fluorine.  When  the 
glass  bulb  was  filled  to  about  three-fourths  of 
its  capacity,  the  valves  were  closed.  The  liquid 
oxygen  surrounding  the  glass  bulb  was  then 
evaporated  under  a  very  low  pressure,  and  the 
temperature  sank  to  —  210° ;  but  even  at  this  low 
temperature  the  fluorine  retained  its  characteristic 
mobility.  In  a  second  experiment  the  liquid  flu- 
orine was  introduced  into  a  glass  tube,  which  was 
afterward  sealed  and  kept  for  some  time  at  a  tem- 
perature of  -  210°,  but  there  were  no  indications 
of  solidification. 

Liquefaction  of  Hydrogen 

Of  the  various  gases  known,  hydrogen  has  pre- 
'sented  the  most  difficult  problem  to  the  experi- 
menters on  the  liquefaction  of  gases.  During  the 
last  two  decades  numerous  attempts  have  been 
made  to  liquefy  this  gas.  Reference  has  already 
been  made  to  the  experiments  of  Cailletet  and 
Pictet,  in  which  hydrogen  was  probably  obtained 


222  LIQUEFACTION   OF  GASES 

in  the  form  of  a  very  fine  mist  (pp.  1 19,  135).  Wro- 
blewski  and  Olszewski  modified  these  experiments 
somewhat  by  cooling  the  gas  with  liquid  oxygen, 
and  then  allowing  the  gas  to  expand  (pp.  143,  164). 
In  these  observations  there  can  be  no  doubt  as  to 
the  formation  of  a  mist  of  liquid  hydrogen.  Both 
of  these  experimenters  endeavored  to  determine 
the  critical  constants  and  boiling  point  of  this  gas. 
In  1894  Dewar1  attacked  the  problem  from  a 
different  standpoint.  Realizing  that,  with  liquid 
oxygen  and  liquid  air  as  refrigerants,  the  tempera- 
ture could  not  be  sufficiently  reduced  for  the  lique- 
faction of  hydrogen,  he  endeavored  to  obtain  a 
liquid,  the  critical  temperature  and  boiling  point 
of  which  are  considerably  lower  than  those  of  air 
and  oxygen.  This  he  thought  could  be  accom- 
plished by  liquefying  a  mixture  of  hydrogen  and 
nitrogen.  In  regard  to  the  efficiency  of  this 
method  the  author  says :  "  One  thing  can,  how- 
ever, be  proven  by  the  use  of  the  gaseous  mixture 
of  hydrogen  and  nitrogen ;  viz.,  that  by  subjecting 
it  to  a  high  compression  at  a  temperature  of 
-  200°,  and  expanding  the  resulting  liquid  into' 
the  air,  a  much  lower  temperature  than  anything 
that  has  yet  been  recorded  up  to  the  present  time 
can  be  reached.  This  is  shown  by  the  fact  that 

1  Chem.  Neivs,  70,  p.  115. 


LIQUEFACTION   OF   HYDROGEN  223 

such  a  mixed  gas  gives,  under  the  conditions,  a 
paste  or  jelly  of  solid  nitrogen,  evidently  giving  off 
hydrogen,  because  the  escaping  gas  burns  fiercely. 
Even  when  hydrogen  containing  from  two  to  five 
per  cent  of  air  is  similarly  treated,  the  result  is  a 
white  solid  mass  (solid  air),  along  with  a  clear 
liquid  of  low  density  which  is  so  exceedingly  vola- 
tile that  no  known  device  for  collecting  it  has 
been  successful." 

During  the  next  year  Dewar l  extended  his  obser- 
vations on  the  liquefaction  of  hydrogen  (p.  198). 
He  says :  "  Hydrogen,  cooled  to  -  200°,  was 
forced  through  a  fine  nozzle  under  a  pressure  of 
140  atmospheres,  and  yet  no  liquid  jet  could  be 
seen.  If,  however,  hydrogen,  previously  cooled  by 
a  bath  of  boiling  air,  is  allowed  to  expand  from  a 
pressure  of  200  atmospheres  over  a  regenerative 
coil,  a  liquid  jet  can  be  seen  after  the  circulation 
has  continued  for  a  few  minutes,  along  with  a 
liquid  which  is  in  rapid  rotation  in  the  lower  part 
of  the  vacuum-vessel.  The  liquid  did  not  accumu- 
late, owing  to  its  low  specific  gravity  and  the  rapid 
current  of  gas.  These  difficulties  will  doubtless 
be  overcome  by  the  use  of  a  differently  shaped 
vacuum-vessel,  and  by  better  isolation." 

In  May,  1898,  Dewar  obtained  liquid  hydrogen 

1  Proc.  Roy.  Inst.,  15,  p.  146. 


224  LIQUEFACTION   OF   GASES 

for  the  first  time  in  a  static  condition.1  The 
method  of  procedure  was  similar  to  that  which  has 
just  been  described.  Hydrogen  cooled  to  a  tem- 
perature of  —205°,  and  under  a  pressure  of  180 
atmospheres,  was  allowed  to  escape  continuously 
from  the  nozzle  of  a  coil  of  pipe,  at  the  rate  of 
from  ten  to  fifteen  cubic  feet  per  minute,  into  a 
doubly  silvered  vacuum-vessel  of  special  construc- 
tion. The  space  surrounding  this  vessel  was  kept 
at  a  temperature  below  —200°.  Soon  after  the 
operation  was  begun,  liquid  hydrogen  began  to 
drop  from  this  vacuum-vessel  into  a  second  vessel 
which  was  doubly  isolated,  in  that  it  was  sur- 
rounded by  a  third  vacuum-vessel.  Within  five 
minutes  about  twenty  cubic  centimetres  of  liquid 
hydrogen  had  collected  in  the  second  bulb.  The 
experiment  was  interrupted  at  this  point  by  the 
solidification  of  air  in  the  pipes.  The  liquid 
obtained  was  clear  and  colorless,  and  showed  a 
well-defined  meniscus.  No  provision  was  made  in 
this  experiment  for  determining  the  boiling  point  of 
liquid  hydrogen,  but  the  author  calls  attention  to 
an  observation  which  shows  that  the  temperature 
of  liquid  hydrogen  under  atmospheric  pressure  is 
extremely  low.  A  long  piece  of  glass  tubing, 
sealed  at  one  end  and  open  at  the  other,  was 

lProc.  Roy.  Soc.,  63,  p.  256,  1898. 


LIQUEFACTION   OF    HYDROGEN  225 

cooled  by  immersing  the  closed  end  in  liquid 
hydrogen.  The  portion  of  the  tube  immersed  in 
the  liquid  was  immediately  filled  with  solid  air. 

A  few  months  later  Dewar  determined  the  boil- 
ing point  and  density  of  liquid  hydrogen.1  The 
boiling  point  was  measured  by  means  of  a  platinum 
resistance  thermometer,  and  was  found  to  be  about 
-  238°.  This  is  a  few  degrees  higher  than  the 
values  given  by  Wroblewski  and  Olszewski.  The 
author  thinks  that  the  critical  temperature  of 
hydrogen  is  about  —  225°,  and  the  critical  pressure 
about  fifteen  atmospheres.  The  density  of  liquid 
hydrogen  was  determined  by  measuring  the  vol- 
ume of  gas  which  is  given  off  when  ten  cubic  cen- 
timetres of  the  liquid  are  allowed  to  evaporate. 
The  result  of  the  experiment  gave  a  density  of 
0.07  for  liquid  hydrogen,  which  is  only  about  one- 
fourteenth  that  of  water. 

During  the  present  year  Dewar  has  made  a 
series  of  observations  on  the  temperature  obtained 
by  evaporating  liquid  hydrogen  under  reduced 
pressure.2  When  the  liquid  was  evaporated  under 
a  pressure  of  25  millimetres  of  mercury,  there 
were  no  indications  of  solidification  or  loss  of 
mobility.  The  temperature  according  to  the  plati- 
num resistance  thermometer  was  —  239°. i,  which 

1  Chem.  News,  77,  pp.  261  and  282,  1898. 
vibid.y  79,  p.  61,  1899. 
Q 


226  LIQUEFACTION    OF   GASES 

is  only  one  degree  lower  than  the  boiling  point 
The  author  says  that  the  temperature  thus  obtained 
should  have  been  five  or  ten  degrees  below  the 
boiling  point,  and  adds  that  the  experiment  will  be 
repeated  with  larger  quantities  of  liquid  hydrogen. 

Quite  recently  Dewar  has  repeated  the  experi- 
ments on  the  boiling  point  of  hydrogen,1  and  ob- 
tained a  value  somewhat  lower  than  that  obtained 
in  the  previous  experiments.  The  author  pre- 
pared 250  cubic  centimetres  of  liquid  hydrogen 
for  these  observations.  The  temperature  of  hy- 
drogen, boiling  under  the  atmospheric  pressure, 
was  determined  by  means  of  a  rhodium-platinum 
resistance  thermometer  and  found  to  be  —  246°. 
This  value  is  8°  lower  than  that  obtained  by 
means  of  the  platinum  resistance  thermometer. 

In  an  addendum  to  this  paper  the  author  calls 
attention  to  some  measurements  made  by  means 
of  a  hydrogen  thermometer  under  reduced  press- 
ure. This  thermometer  gave  -  182°.  5  for  the 
boiling  point  of  oxygen,  and  —  252°  for  the  boil- 
ing point  of  hydrogen.  If  this  value  is  the  true 
boiling  point  of  hydrogen,  it  is  likely  that,  by  evap- 
orating liquid  hydrogen  under  reduced  pressure, 
the  temperature  can  be  lowered  to  within  ten  or 
twelve  degrees  of  the  absolute  zero. 

1  Chem.  News,  March  24,  1899,  p.  133. 


LIQUEFACTION    OF   HELIUM  227 

Liquefaction  of  Helium 

After  an  elaborate  series  of  experiments  with  a 
view  of  liquefying  this  gas,  Olszewski  remarked, 
"  As  far  as  my  experiments  go,  helium  remains  a 
permanent  gas,  and  apparently  is  much  more  diffi- 
cult to  liquefy  than  hydrogen"  (p.  217).  After 
obtaining  liquid  hydrogen  in  a  static  condition, 
Dewar 1  placed  a  sealed  glass  tube  containing 
helium  in  the  liquid  hydrogen.  A  colorless  liquid 
immediately  condensed  on  the  sides  of  the  tube. 
By  placing  the  same  tube  in  liquid  air,  boiling 
under  reduced  pressure,  no  condensation  was  ob- 
served. The  author  concluded  that  the  boiling 
point  of  helium  is  very  close  to  that  of  hydrogen. 

Some  Recently  Discovered  Gases 

During  the  last  year  Ramsay  and  Travers  have 
reported  three  new  gases  in  the  atmosphere.  The 
first  of  these  gases,2  which  the  authors  designated 
as  "  krypton,"  was  obtained  by  evaporating  750 
cubic  centimetres  of  liquid  air,  and  collecting  the 
gas  from  the  last  ten  cubic  centimetres.  After 
removing  the  oxygen  and  nitrogen  from  this  gas, 
a  residue  of  26.2  cubic  centimetres  remained  in 
the  vessel.  The  residual  gas  had  a  spectrum  dif- 

lProc.  Roy.  Soc.,  63,  p.  257,  1898. 
*Ibid.,  p.  405,  1898. 


228  LIQUEFACTION   OF  GASES 

ferent  from  that  of  argon,  and  was  considered  by 
the  authors  as  an  elementary  substance. 

The  other  two  gases,  which  were  called  by  the 
authors  "  the  companions  of  argon,"  were  obtained 
from  liquid  argon.1  The  first  portions  of  gas 
which  escape  when  liquid  argon  is  allowed  to 
evaporate  were  collected  by  Ramsay  and  Travers, 
and  sparked  with  oxygen  gas ;  after  which  the 
excess  of  oxygen  was  removed.  The  residual  gas 
gave  a  spectrum  different  from  that  of  argon  and 
krypton,  and  was  called  "  neon." 

During  the  evaporation  of  the  liquid  argon  a 
white  solid  separated.  After  the  liquid  had  been 
completely  evaporated,  the  solid  residue  was  vapor- 
ized, and  the  gas  collected.  This  gas  was  found 
to  be  different  from  those  just  described,  and  was 
called  "metargon." 

It  is  evident  from  the  preceding  account  that 
these  gases,  mixed  with  air,  argon,  etc.,  have  all 
been  liquefied.  The  authors  state  that  "while 
metargon  is  a  solid  at  the  temperature  of  boiling 
air,  krypton  is  probably  a  liquid,  and  more  volatile 
at  that  temperature."  Liquid  neon  is  somewhat 
more  volatile  than  liquid  argon. 

During  this  same  year  Brush  published  an  ac- 
count of  a  supposed  new  gas.2  The  gas  was 

1  Proc.  Roy.  Soc.,  63,  p.  437,  1898. 

2  Read  before  the  American  Association  for  the  Advancement  o* 
Science,  Aug.  23,  1898. 


TABLE   OF   PHYSICAL  CONSTANTS          229 

obtained  by  exhausting,  to  a  high  degree,  pulver- 
ized soda  glass.  The  resulting  gas  was  found  to 
be  a  much  better  conductor  of  heat  than  any  other 
known  gas.  At  a  pressure  of  0.000096  atmos- 
pheres the  conducting  capacity  was  twenty  times 
that  of  hydrogen.  The  author  says  :  "  Evidently  a 
new  gas  of  enormous  heat-conducting  capacity  was 
present,  mixed-with  the  last  small  traces  of  air." 
From  measurements  of  the  conductivity  he  con- 
cluded that  the  density  of  the  new  gas  is  only 
about  YO^O  tnat  °f  hydrogen.  Owing  to  the  ex- 
tremely low  density  the  author  suggested  the  name 
"etherion"  for  the  new  gas.  In  case  subsequent 
observation l  should  confirm  the  theory  of  Brush, 
the  new  gas  will  furnish  an  interesting  problem  to 
the  experimenters  on  the  liquefaction  of  gases. 

TABLE  OF  PHYSICAL  CONSTANTS 

The  following  table  contains  the  critical  con- 
stants, boiling  points,  melting  points,  etc.,  of  sub- 
stances which  usually  occur  as  gases,  and  of  some 
of  the  most  common  liquids.  A  few  theoretical 
results  are  also  given  for  some  of  the  heavier 
metals.  It  frequently  happens  that  the  results 
obtained  by  one  experimenter  do  not  agree  with 
those  obtained  by  another.  This  is  especially  true 

1  Crookes  has  already  suggested  that  this  gas  may  be  highly 
exhausted  aqueous  vapor.  — Chem.  News,  78,  p.  221,  1898. 


230 


LIQUEFACTION    OF   GASES 


in  regard  to  the  critical  constants.  The  names  in 
the  right-hand  column  are  given  as  authority  for 
the  critical  constants  chosen.1 


Substance 

Critical 
Tempera- 
ture 

Criti- 
cal 
Press- 
ure 

Boiling 
Point 

Freez- 
ing 
Point 

Color  of 
Liquid 

Observer 

Acetone 

+  237°-5 

60 

+   56°.5 

Colorless 

Sajotschewski 

Acetylene  .     . 

+  37°-5 

68 

.. 

Colorless 

Ansdell 

Air     .... 

_ 





Alcohol.     .     . 

+243^.6 

62.7 

+    78°-3 

-130° 

Colorless 

Ramsay  and  Young 

Ammonia   . 

+  130° 

—  33°-7 

-  75° 

Colorless 

Dewar 

Argon    .     .     . 

—  121° 

50.6 

-187' 

-1890.6 

Colorless 

Olszewski 

Arsine    .     .     . 

—  55° 

—  119° 

Colorless 

Carbon  dioxide 

+    31° 

75 

-65° 

Colorless 

Andrews 

Carbon    disul- 

phide  .     .     . 

+2710.8 

74-7 

+  46° 

-110° 

Colorless 

Sajotschewski 

Carbon     mon- 

oxide . 
Chlorine      .     . 

-14.0 

+  141° 

to 

—190° 
-  36°.  6 

-207° 

-102° 

Colorless 
Yellow 

Wroblewski 
Dewar 

Chloroform 

+260° 

54 

+   61 

Colorless 

Sajotschewski 

Cyanogen   .     . 
Ether      .     .     . 

+  195°-  5 

61.7 
40 

-    21° 

+    35 

-  34°-4 

Colorless 
Colorless 

Dewar 
Ramsay 

Ethylene 
Fluorine      .     . 

+    10D.I 
—  I20°(?) 

4o(?) 

—  102°.5 

—187° 

-169 

Colorless 
Yellow 

Dewar 
Moissan  and  Dewar 

Gold.     .     .     . 

+4300° 

+  1035° 

Calculated  by  Guldberg 

Helium  .     .     . 

t  f 

Colorless 

Dewar 

Hydrochloric 

acid     .     .     . 

+5i°.25 

86 

—  35° 

—  n6° 

Colorless 

Ansdell 

Hydrogen  .     . 

—  252° 

Colorless 

Dewar 

Hydrogen  sul- 

phide .     .     . 

+  100°.  2 

92 

—  6i°.8 

-  85° 

Colorless 

Dewar 

Iron  .... 
Methane 

+  5200° 

—  95°-  5 

5° 

—164° 

+1500° 

Colorless 

Calculated  by  Guldberg 
Dewar 

Nitric  oxide    . 

-  93°-5 

71.2 

—  153°-6 

-167° 

Colorless 

Olszewski 

Nitrogen 

-146° 

35 

—  194°-5 

—  214- 

Colorless 

Olszewski 

Nitrous  oxide  . 

-  35°-4 

75 

-  87°-9 

Colorless 

Dewar 

Oxygen 

-118° 

5° 

—183° 

Pale  blue 

Wroblewski 

Ozone     .     .     . 

-125° 

Indigo  blue 

Phosphine  . 

—  85° 

T-~O 

Colorless 

Platinum     .     . 

+  7000° 

+  1800° 

Calculated  by  Guldberg 

Sulph.  dioxide 

78-9 

—    8° 

. 

Colorless 

Sajotschewski 

Water    .     .     . 

+358°.1 

-4-100° 

0° 

Colorless 

Nadejdine 

1  For  further  data  and  literature  on  critical  constants,  see  Heil- 
born,  Zeit.  Phys.  Chem.,  7,  p.  602,  1891. 


CONCLUSION 

I.    The  Three  States  of  Matter 

THE  experiments  which  have  been  described 
show  that  all  gases  have  been  condensed  to  the 
liquid  state.  It  has  also  been  shown  that,  with 
very  few  exceptions,  all  gases  have  been  solidified. 
The  results  leave  no  doubt  that  all  of  these  sub- 
stances can  exist  in  the  gaseous,  liquid,  or  solid 
state.  At  the  high  temperatures  which  have 
been  obtained  by  means  of  the  electric  furnace, 
the  densest  solids  have  been  liquefied  and  vola- 
tilized. 

Andrews  says  the  liquid  state  of  matter  forms  a 
link  between  the  solid  and  gaseous  states.  This 
link,  however,  is  frequently  suppressed,  and  the 
solid  passes  directly  into  the  gaseous  condition. 
Iodine  and  arsenic  are  well-known  examples  of 
solids  which,  at  the  ordinary  pressure,  sublime 
directly  to  the  gaseous  state  without  assuming  the 
intermediate  liquid  condition.  Solid  carbonic  acid 
behaves  in  a  similar  manner.  The  melting  points 
of  these  substances  are  higher  than  their  boiling 
points.  If  iodine  crystals  are  placed  in  a  test-tube 

231 


232  LIQUEFACTION   OF   GASES 

under  sulphuric  acid,  and  the  temperature  gradu- 
ally raised,  the  substance  melts  and  does  not  vapor- 
ize. Prytz l  has  shown  that  at  a  pressure  of  five 
atmospheres  solid  carbonic  acid  does  not  sublime, 
but  passes  directly  into  the  liquid  state. 

Any  substance  can  exist  as  a  gas  at  a  much 
lower  temperature  than  that  at  which  it  can  exist 
as  a  liquid.  Below  the  temperature  of  zero  de- 
grees ice  slowly  sublimes.  In  the  far  northern 
regions  the  atmosphere  always  contains  aqueous 
vapor.  Pellat2  has  recently  shown  that  iron  sub- 
limes very  slightly  at  the  ordinary  temperature 
and  pressure.  Under  the  proper  conditions  of 
temperature  and  pressure  all  substances  can  be 
made  to  assume  the  gaseous,  liquid,  or  solid  state. 
The  three  states  of  matter  are  usually  defined  as 
follows :  — 

1.  A   gas   has   neither   form   nor  volume,   but 
tends  to  expand  indefinitely. 

2.  A  liquid  has  a  definite  volume,  but  assumes 
the  form  of  the  vessel  in  which  it  is  contained. 

3.  A  solid  has  a  definite  form  and  volume. 
The  relation  between  the   gaseous   and   liquid 

states  has  already  been  discussed  (Chapter  III). 
The  change  from  one  condition  to  the  other  was 
found  to  be  gradual  and  imperceptible.  There  is 

1  Phil.  Mag.,  39,  p.  308,  1895. 

a  Zeit.fiir  compr.  undjluss.,  Case,  2,  p.,  95,  1898. 


CONCLUSION  233 

no  sharp  dividing  line.  The  same  is  true  of  the 
solid  and  liquid  states.  Their  properties,  in  many 
cases,  are  very  similar.  As  the  pressure  is  in- 
creased, solids  tend  more  and  more  to  assume  the 
form  of  the  vessel  in  which  they  are  contained. 
Crystals  which  have  been  subjected  to  enormous 
pressure  in  the  crust  of  the  earth  are  found  to 
be  distorted  into  various  shapes  without  being 
fractured.  The  crystals  seem  to  flow.  The  mole- 
cules of  solids  are  not  rigidly  fixed  in  definite 
positions  about  which  they  vibrate,  but  in  many 
cases  move  about  throughout  the  entire  sub- 
stance. This  has  been  shown  by  the  experi- 
ments of  Roberts-Austen  on  the  diffusion  of 
metals.1  He  showed  that,  at  a  temperature  of 
250°,  and  even  at  a  temperature  of  100°,  gold 
diffuses  throughout  the  length  of  solid  cylinders 
of  lead.  Similar  results  were  obtained  with  silver 
and  gold  at  a  temperature  of  800°.  The  rate 
of  diffusion  in  such  cases  is,  of  course,  very  low, 
but  the  process  is  similar  to  the  diffusion  of  gases 
and  liquids.2 

1  Trans.  Roy.  Soc.,  187,  p.  383,  1896. 

2  Heydweiller  has  endeavored  to  find  some  evidence  of  critical 
phenomena  between  the  liquid  and  solid  states.     The  change  from 
the  transparent  solid  to  the  liquid,  he  said,  appeared  to  be  gradual, 
and  the  melting  point  increased  with  the  pressure.     The   experi- 
ments were  extended  to  pressures  as  high  as  3500  atmospheres. 
Wied.  Ann.,  64,  p.  725,  1898. 


234  LIQUEFACTION   OF   GASES 

2.    Industrial  Application  of  Liquefied  Gases 

Liquefied  gases  have  been  employed  for  techni- 
cal purposes  in  various  directions.  The  carbonic 
acid  industry  is  well  known.  The  liquid  is  used 
in  the  preparation  of  aerated  waters,  and  in  the 
manufacture  of  salicylic  acid.  Enormous  quanti- 
ties of  carbonic  acid  are  liquefied  annually  by 
various  establishments.  Liquid  sulphurous  acid 
is  now  an  ordinary  product  of  commerce.  When- 
ever the  gaseous  product  is  desired  for  laboratory 
use  or  technical  purposes,  it  is  usually  obtained 
from  the  liquid.  At  present,  about  4,000,000  kilo- 
grams of  this  liquid  are  being  prepared  annu- 
ally. Liquid  acetylene  has  been  introduced  for 
illuminating  purposes.  Nitrous  oxide  is  now  lique- 
fied on  a  large  scale,  and  used  as  an  anaesthetic 
for  minor  surgical  operations,  especially  in  den- 
tistry. Liquefied  gases  are  also  used  in  large 
quantities  for  the  purpose  of  refrigeration.  The 
ammonia  ice-machine  is  now  in  operation  in  most 
cities.  In  this  process  the  temperature  is  lowered 
and  the  water  frozen  by  the  evaporation  of  liquid 
ammonia.  Liquid  sulphurous  acid  has  also  been 
used  for  the  same  purpose.  In  1885  Wroblewski 
said,  "  Liquid  air  will  be  the  refrigerant  of  the 
future."  This  prediction,  of  course,  has  not  yet 
been  fulfilled. 


CONCLUSION  235 

Considerable  has  been  said  and  written  about 
the  use  of  liquefied  gases  as  a  motive  power. 
Numerous  attempts  have  been  made  to  introduce 
engines  or  motors  for  this  purpose,  but  no  great 
success  has  yet  crowned  these  efforts.  The  ex- 
tremely low  temperatures  which  result  from  the 
expansion  of  these  liquids  to  gases  at  the  ordinary 
pressure  are  very  objectionable  in  the  application 
of  the  liquids  as  a  motive  power.  It  is  not  likely 
that  these  liquids  will  prove  of  any  great  service 
where  steam-power  is  practicable  (see  p.  211). 
They  may  prove  to  be  of  considerable  value,  how- 
ever, in  cases  where  steam-power  is  impracticable. 
It  has  already  been  suggested  that  liquid  hydro- 
gen and  liquid  air  may  furnish  a  solution  to  the 
balloon  problem. 

The  industry  of  liquefied  gases  is  growing  rap- 
idly. Every  year  sees  a  wider  application  of  these 
liquids.  A  complete  discussion  of  this  subject, 
however,  does  not  fall  within  the  scope  of  a  work 
of  this  nature.1 

3.    Physiological  Action  at  Low   Temperatures 

Some  interesting  observations  have  been  made 
in  regard  to  the  influence  of  very  low  temperatures 
on  living  organisms.  In  1870  Cohn2  made  use  of 

1  For  further  discussion  of  the  subject,  see  references  on  p.  183. 
2Cohn's  Beitrdge  zur  Biologic  der  Pftanzen,  1870,  2,  p.  221. 


236  LIQUEFACTION   OF   GASES 

freezing  mixtures,  and  subjected  bacteria,  for  a 
period  of  12  hours,  to  temperatures  varying  from 
o°  to—  1 8°  without  destroying  their  activity.  Mel- 
sens1  used  solid  carbonic  acid  and  exposed  yeast 
and  vaccine  lymph  to  a  temperature  of  —  78°  with- 
out destroying  the  life  of  the  organisms.  Pictet 
and  Yung2  subjected  various  bacteria  to  low  tem- 
peratures. They  reduced  the  temperature  by  the 
evaporation  of  liquid  sulphurous  and  carbonic 
acids.  The  organisms  were  subjected  for  20 
hours  to  a  temperature  of  —70°;  for  89  hours  to 
a  temperature  of  —76°;  and  finally  for  20  hours 
to  a  temperature  of  —130°  (=—202  F.).  Yeast 
ferment  showed  no  alterations  under  the  micro- 
scope, but  lost  its  power  of  fermentation.  Bacillus 
anthracis  and  several  other  micro-organisms  re- 
tained their  virulence  when  injected  into  living 
animals. 

In  1885  a  very  elaborate  series  of  experiments 
were  made  by  Coleman  and  McKendrick3  in  re- 
gard to  the  effect  of  low  temperatures  on  certain 
bacteria.  Thirty  samples  of  fresh  meat  were 
placed  in  two-ounce  white  glass  phials.  The 
bottles  were  then  carefully  closed  with  corks 
which  had  been  steeped  in  mastic  varnish,  and  the 

1  Cotnpt.  rend.,  70,  p.  629  ;   and  71,  p.  325. 

*Ibid.,  98,  p.  747,  1884. 

8 Proc.  Roy.  Inst.,  n,  p.  309. 


CONCLUSION 


237 


necks  of  the  corked  bottles  were  immersed  in  mol- 
ten sealing  wax.  The  specimens  were  treated  as 
follows :  — 

6  samples  were  exposed  to  a  temperature  of  -  17°  for  65  hours. 


6  « 

6  « 

6  « 

6  « 


U  it 

it  it 

«  a 


-29 

"  -34 

«   -40 
"   -62 


Within  ten  or  twelve  hours  after  removal  to  a 
warm  room,  signs  of  putrefaction  were  visible  in 
all  of  the  bottles,  and  in  the  course  of  a  few  days 
the  putrefactive  process  was  fully  established. 
Other  samples  were  then  exposed  to  a  temperature 
of  —  83°  for  a  period  of  100  hours  with  similar 
results.  Samples  of  fresh  milk,  which  had  been 
hermetically  sealed  and  subjected  to  a  temperature 
of  —  62°  for  eight  hours,  curdled  when  kept  in  a 
warm  room. 

The  following  observations  were  made  by  sub- 
jecting a  rabbit  to  low  temperatures  :  — 


Temperature 

Pulse 

Respiration 

Before  the  experiment 

99°.2  F. 

1  60  per  min. 

45  per  min. 

After  30  min.  exposure 

to  -  93°  .     .     .     . 

94.2   « 

— 

— 

After  60  min.  exposure 

Scarcely 

to  —  100°      .     .     . 

43.2    « 

40  per  min. 

Perceptible 

238  LIQUEFACTION   OF   GASES 

In  this  condition  reflex  action  became  almost 
imperceptible.  When  placed  in  a  warm  room  the 
animal  completely  recovered. 

The  effect  of  low  temperatures  on  cold-blooded 
animals  is  entirely  different  from  that  on  warm- 
blooded animals.  The  author  states  that,  at  low 
temperatures,  a  frog  became  as  hard  as  a  stone  in 
from  ten  to  twenty  minutes,  while  the  warm-blooded 
animal  produced  within  itself  sufficient  heat  to 
enable  it  to  remain  soft  and  comparatively  warm 
during  an  exposure  for  one  hour  to  a  temperature 
of  —  100°  F.  The  production  of  heat,  however, 
was  not  equal  to  the  loss,  and  the  animal  was  con- 
tinually losing  ground ;  the  bodily  temperature 
having  decreased  56°  during  the  exposure. 

In  1893  Pictet1  made  a  second  series  of  exper- 
iments. He  describes  the  struggle  of  nature 
against  external  attacks  as  follows  :  — 

When  a  dog  is  placed  in  a  copper  receiver  which 
is  cooled  down  to  from  —  60°  to  —  90°,  its  temper- 
ature rises  about  one-half  degree  during  the  first 
ten  minutes.  After  ninety  minutes  the  tempera- 
ture falls  one  degree.  Then  follows  a  point  where 
the  struggle  is  given  up;  the  temperature  falls  rap- 
idly, and  the  animal  dies  suddenly.  The  author 
made  similar  experiments  by  exposing  his  arm  to 

lChemiker  Zeitting,  1893,  p.  1337;    Chem.  News,  68,  p.  312. 


CONCLUSION  239 

low  temperatures.  The  only  pain  occurs  within 
the  arm  on  the  periosteum,  the  epidermis  expe- 
riencing no  pain  whatever. 

All  insects  resist  a  temperature  of  —  28°,  but 
not  —  35°.  Myriapods  resist  a  temperature  of 
-50°,  and  snails  —  120°.  The  eggs  of  birds  lose 
their  vitality  at  —  2°  or  —  3°,  the  eggs  of  ants  at 
o°,  and  the  eggs  of  the  silkworm  at  —  40°.  In- 
fusoria died  at  —  90°,  and  bacteria  retained  their 
virulence  after  an  exposure  to  a  temperature  of 
-  213°.  The  temperature  in  the  case  of  the  bac- 
teria was  lowered  by  means  of  frozen  atmospheric 
air. 

In  1894  Pictet1  continued  his  observations,  and 
exposed  himself  to  a  temperature  of  —  110°.  The 
body  was  well  protected  by  clothing  during  this 
exposure,  and  the  legs  were  kept  in  motion.  Pictet 
says  that,  for  a  number  of  years  previous  to  this 
exposure,  he  had  been  suffering  from  indigestion, 
and  then  adds  that  the  exposure  to  this  low  tem- 
perature effected  almost  a  complete  cure;  He 
suggests  that  the  influence  of  low  temperatures 
on  physiological  action  may  prove  to  be  of  great 
therapeutic  value. 

Dewar2  states  that  McKendrick  tried  the  effect 
of  low  temperatures  on  the  spores  of  micro-organ- 

1  Compt.  rend.,  119,  p.  1016. 

2  Chem.  News,  67,  p.  211,  1893. 


240  LIQUEFACTION   OF   GASES 

isms.  Samples  of  flesh,  blood,  milk,  and  similar 
substances  were  sealed  in  glass  tubes  and  exposed 
for  a  period  of  one  hour  to  a  temperature  of 
-  182°.  On  standing  at  the  ordinary  temperature 
for  several  days  these  substances  became  putrid. 
Seeds  of  different  kinds  germinated  after  being 
exposed  to  a  temperature  of  —  182°.  Dewar  con- 
siders the  experiments  with  seeds  as  an  evidence 
in  favor  of  the  possibility  of  Lord  Kelvin's  sug- 
gestion, that  life  may  have  been  brought  to  the 
newly  cooled  earth  upon  a  seed-bearing  meteorite. 


4.    Properties  of  Matter  at  Low   Temperatures 

At  the  low  temperatures  obtained  by  the  evap- 
oration of  liquid  air,  etc.,  the  properties  of  most 
substances  are  materially  modified.  All  organic 
compounds  and,  with  very  few  exceptions,  all 
inorganic  compounds,  are  solids  at  that  tempera- 
ture. Rubber  placed  in  liquid  air  loses  its  elas- 
ticity and  becomes  as  brittle  as  glass,  but  regains 
its  original  condition  when  the  temperature  is 
allowed  to  rise.  Tin  and  many  other  metals  also 
become  very  brittle.  Kreutz  l  has  shown  that  the 
power  of  absorbing  light  is  considerably  modified 
at  low  temperatures.  Many  substances  (mercuric 

1  Phil.  Mag.  [5],  39,  p.  209. 


CONCLUSION  241 

iodide,  mercuric  oxide,  etc.)  change  color  under 
such  conditions. 

Pictet1  and  Dewar2  have  investigated  the  in- 
fluence of  low  temperatures  on  the  phenomenon 
of  phosphorescence.  Many  substances  lose  their 
power  of  phosphorescence  at  low  temperatures, 
while  other  substances,  which  exhibit  only  a  feeble 
phosphorescence  at  the  ordinary  temperature,  be- 
come more  phosphorescent.  A  temperature  of 
—  80°  is  sufficient  to  stop  all  sensible  emission 
from  previously  excited  calcium  sulphide,  but  it 
does  not  prevent  the  unexcited  calcium  sulphide 
from  absorbing  light-energy  which  can  be  evolved 
at  higher  temperatures. 

Zakrzewski  3  has  shown  that  the  specific  heat  of 
silver  changes  about  three  per  cent  in  the  interval 
from  o°  to  — 100°.  Important  results  have  also 
been  obtained  by  Dewar  and  his  associates  on  the 
resistance  of  metals  at  low  temperatures.4  The 
resistance  of  any  metal  to  the  passage  of  the  elec- 
tric current  decreases  with  decreasing  temperature. 
This  law,  however,  does  not  hold  true  for  alloys. 
Dewar  says  :  "  The  results  point  to  the  conclusion 
that  pure  metals  have  no  resistance  near  the  abso- 

1  Compt.  rend.,  Sept.  24,  1894. 

2  Proc.  Roy.  Inst.,  14,  p.  665,  1895. 

3  Phil.  Mag.  [5],  39,  p.  191. 

4  See  references  on  p.  178. 


242  LIQUEFACTION   OF  GASES 

lute  zero  of  temperature.  With  alloys  there  is 
little  change  in  resistance.  In  the  case  of  carbon 
the  resistance  decreases  with  increasing  tempera- 
ture. At  the  temperature  of  the  electric  arc,  car- 
bon appears  to  have  no  resistance." 

Some  interesting  observations  have  been  made 
on  chemical  action  at  low  temperatures.  Dewar 
says  :  "  At  a  temperature  of  —  200°  the  molecules 
of  matter  seem  to  be  drawing  near  to  what  might 
be  called  the  '  death  of  matter '  so  far  as  chemical 
action  is  concerned."  At  this  temperature  yellow 
phosphorus  and  liquid  oxygen  show  no  signs  of 
reaction.  In  1861  Loir  and  Drion1  showed  that 
liquid  ammonia  in  contact  with  concentrated  sul- 
phuric acid  does  not  react  at  first.  Most  of  the 
more  recent  experimenters  on  the  liquefaction  of 
gases  have  made  observations  on  chemical  action 
at  low  temperatures.  The  references  in  most  cases 
have  already  been  given.  In  general,  chemical 
action  ceases  under  these  conditions.  Metallic 
sodium  and  potassium  can  be  thrown  into  liquid 
oxygen  without  action.  Pictet2  has  shown  that 
sodium  does  not  react  with  aqueous  hydrochloric 
acid  (15  %  solution)  at  a  temperature  of  —  80°. 

In  some  cases,  however,  chemical  action  takes 
place  at  very  low  temperatures.  Liquid  ethylene 

1  Phil.  Mag.  [4],  20,  p.  202. 

2  Compt.  rend.,  115,  p.  814,  1894. 


CONCLUSION  243 

reacts  with  chlorine  and  bromine  at  a  tempera- 
ture of  —  102°. 5.  Dewar1  has  shown  that  photo- 
graphic action  takes  place  at  a  temperature  of 
-  1 80°.  The  photographic  action  seems  to  be 
reduced  by  about  80  per  cent.  The  author  states 
that  "  it  is  certain  that  the  Eastman  film  is  fairly 
sensitive  to  photographic  action  at  a  temperature 
of  —  200°. "  Quite  recently  it  has  been  shown  that 
liquid  fluorine  at  a  temperature  of  •-  187°  reacts, 
with  evolution  of  light  and  heat,  with  hydrogen, 
benzene,  turpentine,  etc. 

The  preceding  observations  merely  indicate  the 
various  directions  in  which  liquefied  gases  have 
been  employed.  More  than  a  century  ago  the  great 
Lavoiser  predicted  that,  were  the  earth  suddenly 
placed  in  a  very  cold  region,  the  atmosphere  would 
cease  to  exist  as  an  invisible  fluid,  but  would  return 
to  the  liquid  state,  and  new  liquids,  of  which  we 
have  no  knowledge,  would  be  produced.  This  pre- 
diction has  been  thoroughly  confirmed.  One  by 
one  the  various  gases  have  been  condensed  to  the 
liquid  state,  and  the  term  "  permanent  gas "  has 
lost  its  significance.  Along  with  the  development 
of  the  methods  employed  in  the  liquefaction  of 
gases,  new  industries  of  great  commercial  value 
have  been  opened  up.  The  extremely  low  tem- 

1  Proc.  Roy.  Inst.,  14,  p.  665. 


244  LIQUEFACTION    OF   GASES 

peratures  which  can  be  obtained  by  means  of  these 
liquids  have  broadened  the  range  of  scientific  re- 
search. Numerous  and  important  observations  in 
this  direction  have  already  been  made,  yet  the 
investigations  at  low  temperatures  are  only  in  their 
infancy.  For  many  years  the  scientific  world  has 
been  speculating  in  regard  to  the  probable  condition 
and  properties  of  matter  at  the  absolute  zero  of 
temperature,  —  a  temperature  which  experimen- 
ters have  sought  in  vain  to  reach.  Every  year, 
however,  shortens  the  distance  to  travel,  and  at 
present  only  a  few  degrees  separate  us  from  the 
desired  goal. 


INDEX   TO   AUTHORS 


Addams,  39-40. 

Aime,  43-44. 

Altschul,  92. 

Amagat,  69,  87,  98-102,  112. 

Am  on  tons,  9. 

Andrews,  3,  14,  18,  20,  55,  63 

70-82,   84,   94.   96,    108, 

no,  115,  230,  231. 
Ansdell,  83,  85,  230. 
Arago,  38,  66. 
Avenarius,  85. 

Becquerel,  171. 

Berthelot,  61-62,  114,  116,  120. 

Bianchi,  59. 

Boerhaave,  7-9. 

Boyle,  7,  96. 

Brush,  228,  229. 

Bussy,  28-29,  64. 

Cagnaird  de  la  Tour,  18-21, 
55,  70. 

Cailletet,  3,  4,  69,  82,  87,  91, 
114,  115-120,  136,  137, 
152,  187,  214,  216,  221. 

Chappuis,  137,  160. 

Charles,  9,  10,  n. 

Clark,  87,  92. 

Clausius,  in,  112,  181. 

Clouet,  17. 

Cohn,  235. 

Colardeau,  82,  91. 

Coleman,  186-187,236. 

Colladon,  31-32. 

Crookes,  94,  229. 

Cullen,  181. 


Dalton,  10,  n,  12,  181. 

Darwin,  181. 

Davy,  22,  23,  24,  27. 

Deleuil,  113. 

Despretz,  65. 
65,    Deville,  113,  120. 
109,    Dewar,  4,   10,   83,   143,  145,  152, 
167-178,  187, 197-199,  218- 
221,  221-227,  230,  239,  240, 
241,  242,  243. 

Dickson,  178. 

Drion,  63-64,  70,  242. 

Dufour,  134. 

Duhem,  84. 

Dulong,  38,  66. 

Dumas,  50,  113,  114. 

Ewing,  192. 

Faraday,  3,  16,  22-27,  28,  40,  44- 
45,  56,71,171. 

Fleming,  178. 
Fourcroy,  15. 


"3. 

138, 


Gay  Lussac,  10,  n,  12,  13,  96,  181, 

204. 

Giffard,  182. 
Gorrie,  181. 
Gouy,  88. 
Guericke,  6. 
Guldberg,  230. 
Guy  ton  de  Morveau,  15. 

Hampson,  186,  192-195,  199. 

Hannay,  88,  89,  92,  93,  94. 
Hautefeuille,  137,  160. 

245 


246 


INDEX   TO   AUTHORS 


Heen-Liittich,  88, 
Heilborn,  82,  230. 
van  Helmont,  6. 
Heydweiller,  233. 
Him,  112. 
Hogarth,  88,  89. 
Houston,  183,  184,  185. 

Jamin,  90,  91. 

Joule,  13,  112,  181,  202,  205. 

Kamerlingh-Onnes,  178-180,  187. 
Kelvin     (Lord).        See     William 

Thomson. 
Kirk,  182. 
Kreutz,  240. 
Kuenen,  83. 

Lavoisier,  10,  243. 

Leslie,  31. 

Linde,    182,    186,    187-192,    193, 

199,   210. 

Loir,  64,  242. 

Marchant,  182. 

Mariotte,  7. 

van  Marum,  14,  65. 

Mascart,  120. 

Mathias,  87. 

Maugham,  40. 

Maxwell,  70. 

Mayer,  181,  203,  204. 

McKendrick,  236,  239. 

Melsens,  236. 

Mendeleeft,  64-65,  70,  71. 

Miller,  71,  72. 

Mitchell,  42. 

Moissan,  218-221,  230. 

Monge,  17. 

Nadejdine,  230. 
Natanson,  166. 
Natterer,  53,  56-61,  66,  67. 
Nernst,  211. 
Northmore,  17,  18. 


Olszewski,  4,  137-142,  143,  152- 
167,  187,  213-218,  220,  222, 
225,  227, 230. 

Paris,  23. 

Pawlewski,  83. 

Pellat,  232. 

Perkins,  27,  28,  42. 

Pictet,  i,  3,  4,  31,  113,  114,  115, 
118,  120-137,  152,  178,  221, 
236,  238,  239,  241,  242. 

Postle,  182. 

Pouillet,  66. 

Preston,  68. 

Prytz,  232. 

Ramsay,  87,  89,  90,  213,  217,  227, 

228,  230. 

Rankine,  112,  181. 
Rayleigh,  210. 
Recknagel,  112. 
Regnault,  67,  69. 
Ritchie,  59. 
Roberts-Austen,  233. 
Roscoe,  115. 
Rowlands,  205. 
Rumford  (Count),  13. 

Sajotschewski,  230. 
Sarrau,  112. 
Schorlemmer,  115. 
Siemens,  182. 
Silliman,  41,  42. 
Solvay,  182. 
Soubeiran,  50. 
Stromeyer,  16. 

Thenard,  16,  38. 

Thiesen,  87. 

Thilorier,  33-39,  40,  42,  45,  51,  62, 

76,  181. 

Thomson,  J.,  108. 
Thomson,  William,  12,  13, 112,  181, 

202,  240. 
Torrey,  41-42. 
Traube,  J.,  112. 


INDEX   TO  AUTHORS 


247 


Travers,  227,  228. 
Tripler,  186,  199-202. 
Tyndall,  23. 

Vanquelin,  15. 
Villard,  92. 
Violi,  112. 

van  der  Waals,  84,  96,  105-112. 
Wallis-Tayler,  181,  182,  183. 


Windhausen,  183,  184. 

Witkowski,  167. 

Wroblewski,    4,    137-142,    143- 

152,  153,  187,  222,  225,  230, 

234- 

Young,  in,  230. 
Yung,  236. 

Zakrewski,  241. 


INDEX   TO   SUBJECTS 


Acetylene,  liquefaction  of,  114.  Carbon  disulphide,  81. 


vapor  pressure  of,  114, 
Adiabatic  expansion,  207,  209. 
Air,  attempts  to  liquefy,  27,  31,  60, 

boiling  point  of,  144. 

density  of  liquid,  177. 

liquefaction  of,  119, 148,  150,  156, 
169,  177,  187-202. 

solidification  of,  172,  177,  225. 
Alcohol,  vaporization  of,  in  closed 

tubes,  18. 

Ammonia,  liquefaction  of,  15,  27, 
29,  62,  8 1. 

solidification  of,  52. 

vapor  pressure  of,  53. 
Argon,  liquefaction  of,  213-216. 

boiling  point  of,  216. 

solidification  of,  216. 
Arsenic,  sublimation  of,  231. 
Arsine,  liquefaction  of,  16,  50. 

solidification  of,  158. 

vapor  pressure  of,  53. 

Benzene,  expansion  of  liquid,  90. 
Boiling  point,  table  of,  230. 

absolute,  65,  71. 
Boyle's  law,  7,  96. 
exceptions  to,  15,  44,  61,  65-69, 

79,  97-102. 

Breaking  stress  of  metals  at  low 
temperatures,  176. 

Calcium   chloride,   solution   of,  in 

alcohol  vapor,  89. 
Carbon  dioxide,  see  Carbonic  Acid. 


thermal  transparency  of,  175. 
Carbonic  acid,  liquefaction  of,  13, 
*7,  25,  33,  40,  41,  42,  56,  60, 62, 
64,  72,  75,  80. 
solidification  of,  37,  40,  42  51  60, 

64. 
Carbon    monoxide,     attempts     to 

liquefy,  43,  54,  60,  62,  71. 
liquefaction  of,  113,  114,  118,  142, 

148. 

solidification  of,  149,  157. 
Chemical  action   at  low  tempera- 
tures, 242-243. 
Chlorine,  liquefaction  of,  17,  22,  23, 

29,  62. 

solidification  of,  158. 
Chlorochromic    acid,    liquefaction 

of,  42. 

action  of  phosphorus  on  liquid,  42. 
Chloroform,  thermal  transparency 

of  liquid,  175. 

Coal  gas,  attempt  to  liquefy,  54. 
Cobaltous  chloride,  solution  of,  in 

alcohol  vapor,  89. 
Critical  point,  condition  of  matter 

at  the,  84-96. 
Critical  pressure,  80,  81-83. 

table  of,  230. 
Critical  temperature,  65,  71,  81-83. 

table  of,  230. 

Cyanogen,  liquefaction  of,  26,  27. 
solidification  of,  27,  52. 


Dielectric  constant,  at  low  tempera- 
tures, 178. 


248 


INDEX   TO   SUBJECTS 


249 


Electric  conductivity  of  metals  at 

low  temperatures,  178. 
Ethane,  attempt  to  solidify,  159. 
Ether,  vaporization    of,    in   closed 
tubes,  18,  19,  20,  81. 

thermal  transparency  of,  175. 
Etherion,  229. 
Ethylene,  liquefaction  of,  48. 

solidification  of,  158. 

thermal   transparency  of  liquid, 

175- 
Euchlorine,  liquefaction  of,  26,  51. 

solidification  of,  51. 
Expansion  of  gases,  influence  of 

temperature  on,  12. 
Explosible  ether,  37. 

Fluoboron,  liquefaction  of,  50. 

Fluorescence,  90. 

Fluorine,  liquefaction  of,  218-221. 

attempt  to  solidify,  221. 

reaction  of,  at  low  temperatures, 

220,  221,  243. 
Fluosilicon,  liquefaction  of,  49. 

Gas,  definition  of,  6,  81,  95,  232. 

kinetic  theory  of,  102-104. 

relation  to  liquid,  84-112. 
Gaseous  mixtures,  critical  constants 
of,  82. 

Helium,  attempts   to  liquefy,  216- 

218. 

liquefaction  of,  227. 
Hydriodic  acid,  liquefaction  of,  49. 

solidification  of,  49. 
Hydrobromic  acid,  liquefaction  of, 

49- 

solidification  of,  49. 
Hydrocarbons,  liquefaction  of,  86, 

187. 
Hydrochloric  acid,  liquefaction  of, 

15,  17,  23,  27,  81. 
solidification  of,  158. 
Hydrochloric  ether,  expansion  of 
liquid,  63. 


Hydrofluoric  acid,  solidification  of, 

158- 
Hydrogen,  attempts  to  liquefy,  40, 

43,  54.  60,  71,  114,  119,  135. 
boiling  point  of,  164,  225,  226. 
density  of  liquid,  225. 
liquefaction    of,    143,    153,   221- 

226. 
Hydrogen    selenide,    solidification 

of,  158. 

Hydrogen  sulphide,  see  Sulphuret- 
ted Hydrogen. 

Ice  machines,  181-183,  234- 

Ice,  sublimation  of,  232. 

Industrial  application  of  liquefied 
gases,  234,  235. 

Iodine,  solubility  of,  in  liquid  car- 
bonic acid,  91,  92. 
liquefaction  of,  232. 

Iron,  sublimation  of,  232. 

Krypton,  227,  228. 

Liquid,  definition  of,  95, 232. 

Marsh  gas,  see  Methane. 
Matter,  properties  of,  at  low  tem- 
peratures, 240-244. 
Mechanical  equivalent  of  heat,  205. 
Melting  point,  table  of,  230. 
Metargon,  228. 
Methane,  liquefaction  of,  114,  145, 

159- 

density  of  liquid,  159. 
solidification  of,  158. 
Muriatic    acid,    see    Hydrochloric 
Acid. 

Naphtha,  vaporization  of,  in  closed 

tubes,  18. 
Neon,  228. 
Nitric  oxide,  attempts   to   liquefy, 

43,  54,  62,  71. 
liquefaction  of,  116. 
solidification  of,  158. 


250 


INDEX   TO    SUBJECTS 


Nitrogen,  attempts  to  liquefy,  43, 

54,  71- 

density  of  liquid,  159,  177. 
liquefaction  of,  119,  142,  148, 159, 

177. 

solidification  of,  150,  158. 
Nitrogen  tetroxide,  expansion    of 

liquid,  63. 
liquefaction  of,  63. 
Nitrous  oxide,  liquefaction  of,  26, 

52,  56,  60,  72,  8 1. 
solidification  of,  52,  60. 
thermal  transparency  of  liquid, 

175- 

Olefiant  gas,  see  Ethylene. 
Oxygen,  attempts  to  liquefy,  40,  43, 

54,  60,  62,  71. 

absorption  spectrum  of,  172. 
density  of  liquid,  159,  177- 
liquefaction  of,  113, 114,  "8,  128- 
132, 141,  143,  148,  159,  l67,  l69, 

177,  179.  I92-I99- 
magnetic  property  of,  169. 
solidification  of,  134. 
Ozone,  liquefaction  of,  137,  160. 
attempt  to  solidify,  161. 

Phosphine,  liquefaction  of,  49. 
solidification  of,  158. 

Phosphorescence,  at  low  tempera- 
tures, 241. 

Physical  constants,  table  of,  230. 

Physiological  action   at  low  tem- 
peratures, 235-240. 

Potassium   iodide,  solution   of,  in 
alcohol  vapor,  88,  89. 

Propane,  attempt  to  solidify,  159. 


Radiant  matter,  95. 
Refrigerating  machines,  182,  183. 
Regenerative  method  of  refrigera- 
tion, 180-202. 
theory  of,  202-213. 

Silicon  tetrafluoride,  solidification 

of,  158. 

Solid,  definition  of,  232. 
Solids,  diffusion  of,  233. 
solution  of,  in  gases,  88-90. 
solution  of,  in  solids,  233. 
Specific  heat,  of  gases,  203. 
of  metals  at   low  temperatures, 

241. 

Stibine,  solidification  of,  158. 
Sulphur,  solution  of,  in  carbon  di- 

sulphide,  89. 
Sulphur  dioxide,  see    Sulphurous 

Acid. 

Sulphuretted    hydrogen,    liquefac- 
tion of,  15,  25,  52. 
solidification  of,  52. 
Sulphurous    acid,   liquefaction   of, 

15,  17,  24,  29,  42,  63. 
solidification  of,  43,  51. 


Temperature,  absolute,  n. 

influence  of,  on  gaseous  volume, 

I,  10. 

Thilorier's  mixture,  39. 


Vacuum  bulbs,  172-175- 
Vapor,  definition  of,  6,  81,  94. 
density  of  saturated,  85-88. 
Vaporization,  heat  of,  29. 


LIGHT  VISIBLE  AND  INVISIBLE: 


A  SERIES  OF  LECTURES  DELIVERED  AT  THE 
ROYAL  INSTITUTION  OF  GREAT  BRITAIN, 


BY 


SYLVANUS  P.  THOMPSON,  D.Sc.,  F.R.S.,  M.R.I., 

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